U.S. patent number 8,235,506 [Application Number 10/567,657] was granted by the patent office on 2012-08-07 for electrostatic suction type fluid discharge method and device for the same.
This patent grant is currently assigned to Konica Minolta Holdings, Inc., National Institute of Advanced Industrial Science and Technology, Sharp Kabushiki Kaisha. Invention is credited to Hironobu Iwashita, Kazuhiro Murata, Shigeru Nishio, Kazunori Yamamoto.
United States Patent |
8,235,506 |
Nishio , et al. |
August 7, 2012 |
Electrostatic suction type fluid discharge method and device for
the same
Abstract
An electrostatic suction type fluid discharge method and device
include a voltage applying means that applies a pulse voltage
between a nozzle and a substrate, the nozzle having a diameter
ranging from 0.01 .mu.m to 25 .mu.m, an upper limit voltage of the
pulse voltage being equal to or greater than a discharge-inducing
minimum voltage. A lower limit first voltage can be provided
immediately before a rise of the pulse voltage, an absolute value
of the lower limit first voltage being set smaller than the
discharge-inducing minimum voltage. A lower limit second voltage
can be provided immediately after a rise of the pulse voltage, an
absolute value of the lower limit second voltage being set smaller
than the discharge-inducing minimum voltage. With this structure,
it is possible to simultaneously achieve miniaturization of nozzle,
discharge of micro fluid droplet, high accuracy for discharge
position, and decrease in drive voltage.
Inventors: |
Nishio; Shigeru
(Yamatokoriyama, JP), Iwashita; Hironobu (Chiyoda-ku,
JP), Yamamoto; Kazunori (Chiyoda-ku, JP),
Murata; Kazuhiro (Chiyoda-ku, JP) |
Assignee: |
Sharp Kabushiki Kaisha (Osaka,
JP)
Konica Minolta Holdings, Inc. (Tokyo, JP)
National Institute of Advanced Industrial Science and
Technology (Tokyo, JP)
|
Family
ID: |
34139373 |
Appl.
No.: |
10/567,657 |
Filed: |
August 6, 2004 |
PCT
Filed: |
August 06, 2004 |
PCT No.: |
PCT/JP2004/011376 |
371(c)(1),(2),(4) Date: |
October 26, 2006 |
PCT
Pub. No.: |
WO2005/014180 |
PCT
Pub. Date: |
February 17, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070101934 A1 |
May 10, 2007 |
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Foreign Application Priority Data
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Aug 8, 2003 [JP] |
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2003-206941 |
Aug 8, 2003 [JP] |
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2003-206944 |
Aug 8, 2003 [JP] |
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2003-206946 |
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Current U.S.
Class: |
347/55; 347/74;
347/73; 347/75 |
Current CPC
Class: |
B05B
5/0255 (20130101); B41J 2/06 (20130101); B41J
2/04588 (20130101); H05K 3/125 (20130101); B41J
2/04576 (20130101); B05C 5/0216 (20130101); H05K
2203/105 (20130101); B05C 11/1034 (20130101); H05K
2203/013 (20130101) |
Current International
Class: |
B41J
2/06 (20060101) |
Field of
Search: |
;347/55,73-83
;118/621,624 ;239/690,706 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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36-013768 |
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Aug 1961 |
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JP |
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63-007946 |
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Jan 1988 |
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JP |
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07-223317 |
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Aug 1995 |
|
JP |
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08-238774 |
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Sep 1996 |
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JP |
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10-052917 |
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Feb 1998 |
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JP |
|
2000-127410 |
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May 2000 |
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JP |
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2001-088306 |
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Apr 2001 |
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JP |
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2002-172786 |
|
Jun 2002 |
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JP |
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2002172786 |
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Jun 2002 |
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JP |
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2004-129699 |
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Apr 2004 |
|
JP |
|
Other References
Koichi Saito; "Theory of the Electrostatic Suction Type Slit Jet";
Electronic Imaging & Devices research Laboratory; vol. 17; pp.
185-193; 1988. cited by other.
|
Primary Examiner: Luu; Matthew
Assistant Examiner: Legesse; Henok
Attorney, Agent or Firm: Edwards Wildman Palmer LLP Conlin;
David G. Tucker; David A.
Claims
The invention claimed is:
1. An electrostatic suction type fluid discharge device which
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle of a discharge head onto a substrate opposite to the nozzle,
wherein: the electrostatic suction type fluid discharge device
comprises line-drawing means for applying a voltage between the
nozzle and the substrate while relatively moving the nozzle and the
substrate so as to carry out line-drawing, the voltage being equal
to or greater than a minimum voltage to induce discharge, that is a
voltage required to start discharge of the fluid, the line-drawing
means controlling a speed of the relative movement so that adjacent
ones of discharge pattern are partly overlaid with each other, in
accordance with a period of intermittent discharge which is
performed when applying a direct current bias voltage equal to or
greater than the minimum voltage to induce discharge and which is
performed at a frequency depending on the direct current bias
voltage and an electric conductivity of the fluid, and the fluid
discharge hole of the nozzle having a diameter ranging from 0.01
.mu.m to 15 .mu.m, and the discharge head discharging the fluid
from the nozzle not by a piezo element and/or a thermal element,
but by electrostatic suction.
2. The electrostatic suction type fluid discharge device, as set
forth in claim 1, wherein; the line-drawing means controls the
speed of the relative movement so that the adjacent ones of
discharge pattern are overlaid with each other by 0.5 to 1.5 times
of a vertical diameter of each pattern, the vertical diameter being
a diameter orthogonal to a direction of the relative movement.
Description
TECHNICAL FIELD
The present invention relates to an electrostatic suction type
fluid discharge method that electrically charges a fluid such as
ink, and discharge the fluid due to suction by an electrostatic
force onto an object such as a substrate. The present invention
also relates to a device for carrying out the method.
BACKGROUND ART
Typical examples of fluid jet methods for discharging a fluid such
as ink onto an object (recording medium) are a piezo type and a
thermal type that are commercially utilized in ink jet printers. In
addition to them, there is an electrostatic suction type method
which applies an electric field to the fluid to be discharged,
causing the fluid to be discharged through a hole (ink discharge
hole, discharge hole) of nozzle.
Such an electrostatic suction type fluid discharge device is
disclosed in, for example, Japanese Examined Patent Publication
Tokkosho 36-13768 (published on Aug. 18, 1961) and Japanese
Laid-Open Patent Application No. 2001-88306 (published on Apr. 3,
2001).
Also, Japanese Laid-Open Patent Application No. 2000-127410
(published on May 9, 2000) discloses a device arranged such that a
nozzle hole is slit-shaped and a protruding needle electrode is
formed on the nozzle hole, and an ink including fine particles is
discharged using the needle electrode.
Japanese Laid-Open Patent Application No. 8-238774 (published on
Sep. 17, 1996) discloses a device in which an electrode for
applying a voltage is provided in an ink container from which an
ink is supplied to a nozzle hole.
The following describes a fluid discharge model in a conventional
electrostatic suction type fluid discharge device.
Design factors of electrostatic suction type fluid discharge
devices, especially of on-demand electrostatic suction type fluid
discharge devices, are conductivity of ink fluid (e.g. specific
resistance of 10.sup.6 to 10.sup.11 .OMEGA.cm), surface tension
(e.g. 0.020 to 0.040N/m), viscosity (e.g. 0.011 to 0.015 Pas), and
applied voltage (electric field). As to the applied voltage, it has
been considered that the voltage applied to the nozzle and the
distance between the nozzle and a counter electrode are
particularly important.
The electrostatic suction type fluid discharge devices utilize
electrofluid instability, as shown in FIG. 32. Placing a conductive
fluid in a uniform electric field, an electrostatic force exerted
on the surface of the conductive fluid causes the surface to be
instable, thereby precipitating the development of a thread
(electro static spinning phenomenon). The electric field on this
occasion is defined as E.sub.0 which is generated when a voltage V
is applied between a nozzle and a counter electrode. The distance
between a nozzle hole at the tip of the nozzle and the counter
electrode is defined as h. A development wavelength .lamda..sub.C
in the aforesaid case can be physically figured out (see, e.g. The
Institute of Image Electronics Engineers of Japan, Vol. 17, No. 4,
1988, pp. 185-193), and the developing wavelength .lamda..sub.C is
represented by the following equation.
.lamda..times..pi..gamma..times. ##EQU00001##
In the equation, .gamma. expresses surface tension (N/m), .di-elect
cons..sub.0 expresses dielectric constant (F/m) in a vacuum, and
E.sub.0 expresses electric field intensity (V/m). If the nozzle
diameter d(m) is shorter than the development does not occur. That
is, the condition of the discharging is defined as follows.
>.lamda..pi..gamma..times. ##EQU00002##
Provided that E.sub.0 is an electric field intensity on the
assumption that a parallel flat plate is adopted, h(m) is the
distance between the nozzle and counter electrode, and V.sub.0 is a
voltage applied to the nozzle, the following equation is given:
##EQU00003##
According to this, d is found as follows.
>.pi..gamma..times..times..times. ##EQU00004##
The fluid discharge devices have typically been required to reduce
the diameter of the nozzle through which ink is discharged, in
order to form finer dots and lines.
However, in the currently-used piezo or thermal type fluid
discharge devices, it is difficult to reduce the nozzle diameter
and discharge, for example, a very small amount of fluid less than
1 pl. This is because, the smaller the nozzle for discharging a
fluid is, the more the pressure required for the discharge
increases.
In addition to the above, in the aforesaid fluid discharge devices,
the miniaturization of droplets contradicts the improvement of
precision, and hence it has been difficult to realize both of these
improvements at the same time. The reason of this will be described
below.
Kinetic energy imparted to the droplet discharged from the nozzle
is in proportion to the cube of the diameter of the droplet.
Therefore, the miniature droplets discharged in a case where the
nozzle is miniaturized cannot attain the kinetic energy sufficient
to resist the air resistance at the time of the discharge, and the
droplets are disturbed by accumulated air or the like. For this
reason, it is not possible to expect precise landing of the
droplets. Moreover, since the effect of the surface tension
increases as the size of the droplets decreases, the vapor pressure
of the droplets increases and an amount of evaporation increases.
Because of this, the miniature droplet causes great loss of mass in
the process of flying, and it hardly remains the form of droplet at
the time of landing.
In addition to the above, according to the aforesaid fluid
discharge model of the conventional electrostatic suction type
fluid discharge devices, the reduction of the nozzle diameter
demands the increase in the electric field intensity required for
the discharge, as the above-described equation (2) shows. The
electric field intensity is, as shown in the equation (3),
determined by the voltage (drive voltage) V.sub.0 applied to the
nozzle and the distance h between the nozzle and counter electrode.
Therefore, the reduction of the nozzle diameter results in the
increase in the drive voltage.
The drive voltage in the conventional electrostatic suction type
fluid discharge devices is very high (not less than 1000V). It is
therefore difficult to achieve the reduction in size and the
density growth, in consideration of leaks and interferences between
the nozzles. The problem becomes serious as the nozzle diameter is
further reduced. A power semiconductor with a high voltage of not
less than 1000V is typically expensive and does not excel in
frequency responsiveness.
In the Japanese Examined Patent Publication 36-13768, the nozzle
diameter is 0.127 mm. The range of the nozzle diameter in Japanese
Laid-Open Patent Application No. 2001-88306 is specified as 50 to
2000 .mu.m, more preferably 100 to 1000 .mu.m.
As to the nozzle diameter, the development wavelength .lamda..sub.c
is worked out as follows, if typical operating conditions of the
conventional electrostatic suction type fluid discharge are
applied: the development wavelength .lamda..sub.c is about 140
.mu.m where the surface tension is 0.020 N/m and the electric field
intensity is 10.sup.7V/m in the aforesaid equation (1).
Consequently, the limit nozzle diameter is 70 .mu.m. It has
therefore been considered that, in a case where the nozzle diameter
is not more than about 70 .mu.m in the aforesaid conditions, the
ink development does not occur even if the field intensity is high
(10.sup.7V/m), unless a countermeasure such as forcible formation
of meniscus by the application of a back pressure is carried out.
In short, it has been considered that the miniaturization of the
nozzle is not compatible with the reduction in the drive
voltage.
As described above, in the conventional fluid discharge devices,
the miniaturization of the nozzle contradicts with the improvement
of precision, and it has been difficult to achieve both of these
improvements. In particular, regarding the electrostatic suction
type fluid discharge devices, it has been considered that the
miniaturization of the nozzle contradicts with the reduction in the
drive voltage.
The present invention is made in view of the foregoing problems,
and an object is to provide an electrostatic suction type fluid
discharge method by which miniaturization of nozzle, discharge of a
small amount of fluid with higher precision of landing position,
and decrease in drive voltage are all achieved. The present
invention also provides a device for carrying out the method.
DISCLOSURE OF INVENTION
In order to attain the foregoing object, an electrostatic suction
type fluid discharge device according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle onto a substrate opposite to the nozzle, wherein: the fluid
discharge hole, provided in the nozzle, has a diameter ranging from
0.01 .mu.m to 25 .mu.m, the electrostatic suction type fluid
discharge device comprises voltage applying means for applying a
pulse voltage between the nozzle and the substrate, an upper limit
voltage of the pulse voltage being equal to or greater than a
minimum voltage to induce discharge, that is a voltage required to
start discharge of the fluid, and a pre-charge voltage is provided
immediately before a rise of the pulse voltage, the pre-charge
voltage having a same polarity as that of the upper limit voltage,
an absolute value of the pre-charge voltage being set smaller than
the minimum voltage to induce discharge.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge method according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle onto a substrate opposite to the nozzle, the fluid discharge
hole, provided in the nozzle, having a diameter ranging from 0.01
.mu.m to 25 .mu.m, the method comprising the step of applying a
voltage between the nozzle and the substrate, the voltage being
equal to or greater than a minimum voltage to induce discharge,
that is a voltage required to start discharge of the fluid, wherein
a pre-charge voltage is provided immediately before a rise of the
voltage, the pre-charge voltage having a same polarity as that of
the voltage, an absolute value of the voltage being set smaller
than the minimum voltage to induce discharge.
With the above structure, the fluid discharge hole provided in the
nozzle has a diameter ranging from 0.01 .mu.m to 25 .mu.m, a local
electric field is generated. Consequently, this miniaturization of
nozzle allows reduction in drive voltage for discharge. Such
reduction of the drive voltage is greatly beneficial to realize
miniaturization of the device while ensuring high density. It may
be obvious but reduction of the drive voltage allows the use of a
low-voltage driver that offers advantageous cost performance. Note
that, there is more detailed description below for this discharge
model carrying out discharge of fluid by generating a local
electric field with a micro nozzle.
Moreover, in the discharge model using the local electric field,
the electric field strength required for discharge depends upon the
converged local electric field strength, and therefore the counter
electrode can be omitted. In other words, it becomes possible to
carry out printing on an insulating substrate without using a
counter electrode, allowing more flexible device arrangement.
Further, it also becomes possible to print on a thick
insulator.
However, the miniaturization of the nozzle described above has such
a problem that, when the discharge amount becomes significantly
small, the discharge response suddenly slows down exponentially.
This makes the high-frequency drive difficult. By increasing the
upper-limit voltage of the pulse voltage applied between the nozzle
and the substrate, the discharge response increases to a certain
degree, allowing the driving to be carried out at relatively
high-frequencies. However, this structure requires a high-voltage
driver for applying a high-voltage to the driving electrode.
Because of this, the cost reduction due to the use of low-voltage
driver, which was the main advantage of the miniaturization of the
nozzle, cannot be attained.
When looking at the discharge response more specifically, it can be
divided into the discharge-start response at the rise of the pulse
voltage and the discharge-end response at the fall thereof.
Therefore, low discharge response implies incapability of control
of discharge amount with high accuracy, precisely dependent upon
the application time of the upper limit voltage.
On the other hand, in the above structure in which the voltage
applying means applies a pulse voltage between the nozzle and the
substrate, and an upper limit voltage of the pulse voltage is set
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid; a pre-charge
voltage is applied immediately before a rise of the pulse voltage,
the pre-charge voltage having a same polarity as that of the upper
limit voltage, an absolute value of the pre-charge voltage being
set smaller than the minimum discharge-inducing voltage. Therefore,
the meniscus surface potential is precharged to a certain degree in
advance before the rise of pulse voltage.
Therefore, after the rise of the pulse voltage, the meniscus
surface potential soon becomes reaches the minimum
discharge-inducing voltage, that is a voltage required to induce
discharge, thereby starting discharge. Therefore, discharge-start
response can be improved. Consequently, the discharge limit
frequency can be improved, making the high-frequency driving
possible.
In order to achieve the above object, an electrostatic suction type
fluid discharge device according to the present invention, which
device discharges by electrostatic suction a fluid, which is
electrically charged by voltage application, from a fluid discharge
hole of a nozzle onto a substrate opposite to the nozzle, is
characterized in that the fluid discharge hole, provided in the
nozzle, has a diameter ranging from 0.01 .mu.m to 25 .mu.m, the
electrostatic suction type fluid discharge device comprises voltage
applying means for applying a pulse voltage between the nozzle and
the substrate, an upper limit voltage of the pulse voltage being
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid, and an
attenuation facilitating voltage is provided immediately after a
fall of the pulse voltage, the attenuation facilitating voltage
having an opposite polarity to that of the upper limit voltage.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge method according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle onto a substrate opposite to the nozzle, the fluid discharge
hole, provided in the nozzle, having a diameter ranging from 0.01
.mu.m to 25 .mu.m, the method comprising the step of applying a
voltage between the nozzle and the substrate, the voltage being
equal to or greater than a minimum voltage to induce discharge,
that is a voltage required to start discharge of the fluid, wherein
an attenuation facilitating voltage is provided immediately after a
fall of the voltage, the attenuation facilitating voltage having an
opposite polarity to that of the voltage.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, so
that the drive voltage can be reduced. This is greatly beneficial
to miniaturization of the device while ensuring high density, and
therefore the same above-described effects as that of the
electrostatic suction type fluid discharge device according to the
present invention is obtained. For example, it allows the use of a
low-voltage driver that offers advantageous cost performance.
Further, in the above structure in which the voltage applying means
applies a pulse voltage between the nozzle and the substrate, and
an upper limit voltage of the pulse voltage is set equal to or
greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid, and an
attenuation facilitating voltage is provided immediately after a
fall of the pulse voltage, the attenuation facilitating voltage
having an opposite polarity to that of the upper limit voltage.
Therefore, the meniscus surface potential is rapidly attenuated
after the fall of the pulse voltage.
Therefore, after the fall of the pulse voltage, the meniscus
surface potential soon becomes lower than the minimum
discharge-maintaining voltage, that is a voltage required to
maintain discharge, and the discharge stops. Therefore,
discharge-end response can be improved. Consequently, the discharge
limit frequency can be improved, making the high-frequency driving
possible.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge device according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle of a discharge head onto a substrate opposite to the nozzle,
wherein: the fluid discharge hole, provided in the nozzle, has a
diameter ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic
suction type fluid discharge device comprises line-drawing means
for applying a voltage between the nozzle and the substrate while
relatively moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
voltage to induce discharge, that is a voltage required to start
discharge of the fluid, the line-drawing means controlling a speed
of the relative movement so that adjacent ones of discharge pattern
are partly overlaid with each other, in accordance with a period of
intermittent discharge which is performed at a frequency depending
on the voltage and an electric conductivity of the fluid.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge method according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle of a discharge head onto a substrate opposite to the nozzle,
the fluid discharge hole, provided in the nozzle, having a diameter
ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic suction type
fluid discharge method comprising the step of applying a voltage
between the nozzle and the substrate while relatively moving the
nozzle and the substrate so as to carry out line-drawing, the
voltage being equal to or greater than a minimum voltage to induce
discharge, that is a voltage required to start discharge of the
fluid, wherein the electrostatic suction type fluid discharge
device controls a speed of the relative movement so that adjacent
ones of discharge pattern are partly overlaid with each other, in
accordance with a period of intermittent discharge which is
performed at a frequency depending on the voltage and an electric
conductivity of the fluid.
With the above structure in which the fluid discharge hole provided
in the nozzle has a diameter ranging from 0.01 .mu.m to 25 .mu.m, a
local electric field is generated in accordance with the discharge
model using a local electric field. On this account,
miniaturization of nozzle achieves a decrease in drive voltage for
discharging. Such reduction of the drive voltage is greatly
beneficial to miniaturization of the device and an increase in
density. It may be obvious but, this reduction of the drive voltage
allows the use of a low-voltage driver that offers advantageous
cost performance.
Moreover, in the discharge model using the local electric field,
the electric field strength required for discharge depends upon the
converged local electric field strength, and therefore the counter
electrode can be omitted. In other words, it becomes possible to
carry out printing on an insulating substrate without using a
counter electrode, allowing more flexible device arrangement.
Further, it also becomes possible to print on a thick
insulator.
However, in the above structure, the discharge response basically
depends upon the electric resistance of fluid (discharge material)
between the electrode in the nozzle and the tip of nozzle, and
therefore, the discharge response may be extremely changed by a
change in electric conductivity of the fluid. In this case, stable
line-drawing may not be performed depending upon the relative speed
between the nozzle and the substrate or the voltage applied between
the nozzle and the substrate. This problem occurs as a consequence
of miniaturization of the diameter of the tip of the nozzle, which
makes the diameter/width of the dot/line formed on the substrate to
be super miniaturized. In addition to this, an increase in electric
resistance as a result of miniaturization of nozzle which results
in deterioration in discharge response also contributes to the
problem. This is a new problem that would not have been an issue in
the conventional discharge amount.
On the other hand, in the above structure, the line-drawing means
applies a voltage between the nozzle and the substrate while
relatively moving the nozzle and the substrate so as to carry out
line-drawing, which voltage is equal to or greater than the minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid. Further, the line-drawing means controls a
speed of the relative movement so that adjacent ones of discharge
pattern are partly overlaid with each other, in accordance with a
period of intermittent discharge which is performed at a frequency
depending on the voltage and an electric conductivity of the fluid.
Therefore, a continuous and stable line-drawing can be performed at
a high speed without causing errors such as an inappropriately
widened line width, while setting the voltage in the vicinity of
the minimum discharge-inducing voltage that is a voltage required
for drawing super micro line.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge device according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle of a discharge head onto a substrate opposite to the nozzle,
wherein: the fluid discharge hole, provided in the nozzle, has a
diameter ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic
suction type fluid discharge device comprises line-drawing means
for applying a voltage between the nozzle and the substrate while
relatively moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
voltage to induce discharge, that is a voltage required to start
discharge of the fluid, the line-drawing means controlling the
voltage so that adjacent ones of discharge pattern are partly
overlaid with each other, the discharge pattern being discharged
intermittently, and being determined depending on a speed of the
relative movement.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which electrostatic suction type
fluid discharge device is electrically charged by voltage
application, from a fluid discharge hole of a nozzle of a discharge
head onto a substrate opposite to the nozzle, wherein the fluid
discharge hole, provided in the nozzle, has a diameter ranging from
0.01 .mu.m to 25 .mu.m; and the electrostatic suction type fluid
discharge device comprises line-drawing means for applying a
voltage between the nozzle and the substrate while relatively
moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid, the line-drawing means controlling the
voltage so that adjacent ones of discharge pattern are partly
overlaid with each other, the discharge pattern being discharged
intermittently, and being determined depending on a speed of the
relative movement.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, so
that the drive voltage can be reduced. This is greatly beneficial
to miniaturization of the device while ensuring high density, and
therefore the same above-described effects as that of the
electrostatic suction type fluid discharge device according to the
present invention is obtained. For example, it allows the use of a
low-voltage driver that offers advantageous cost performance.
Further, in the above structure, the line-drawing means applies a
voltage between the nozzle and the substrate while relatively
moving the nozzle and the substrate so as to carry out
line-drawing, which voltage is equal to or greater than minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid. Here, the voltage applied between the
nozzle and the substrate is so controlled that adjacent ones of
discharge pattern are partly overlaid with each other, which
discharge pattern are discharged intermittently and determined
depending on a speed of the relative movement. Therefore, the
frequency of intermittent discharge can be increased to accommodate
high speed movement, and a continuous and stable line-drawing can
be performed at a desired high speed.
In order to attain the foregoing object, an electrostatic suction
type fluid discharge device according to the present invention
applies a drive voltage by drive voltage apply means between a
nozzle and a discharge target so as to apply an electric charge to
a fluid supplied into the nozzle, and thereby discharges the fluid
from a hole of the nozzle to the discharge target, wherein: the
hole of the nozzle falls within a range between .phi.1 .mu.m and
.phi.5 .mu.m in diameter, the device outputting the drive voltage
under a condition: a voltage value=V.sub.0, and an application
time=t, which are specified as: 130V<V.sub.0[1-exp(-t/RC)] where
R expresses electric resistance of the fluid, and C expresses
electric capacitance between the fluid in a tip of the nozzle and
the discharge target.
In the conventional fluid discharge devices, the miniaturization of
the nozzle requires more intense electric field to cause the fluid
to be discharged, and therefore the miniaturization of nozzle
contradicts with decrease in drive voltage. In contrast, the
present invention has achieved both the miniaturization of nozzle
and the decrease in drive voltage with the use of nozzle whose
diameter is specified within the foregoing range. This structure
was made based on such a new finding that a micro nozzle of
.phi.0.01 .mu.m to .phi.25 .mu.m in diameter causes a local
electric field, which allows the fluid to be discharged by a lower
drive voltage.
Further, the present invention has a structure with a specified
nozzle diameter, ranging from .phi.0.01 .mu.m and .phi.5 .mu.m.
With this structure, the present invention ensures the effect of
decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage for driving nozzle is outputted under a
condition: a voltage value=V.sub.0, and an application time=t,
which are specified as: 130V<V.sub.0[1-exp(-t/RC)], the meniscus
surface potential of the tip of nozzle is securely set to the value
to induce discharge or greater. This increases reliability in
drawing micro dot patterns.
Yet another electrostatic suction type fluid discharge device
according to the present invention applies a drive voltage between
a nozzle and a discharge target by drive voltage supply means so as
to apply an electric charge to a fluid supplied into the nozzle,
and thereby discharges the fluid from a hole of the nozzle to the
discharge target, the hole of the nozzle falling within a range
between .phi.1 .mu.m and .phi.5 .mu.m in diameter, the
electrostatic suction type fluid discharge device is arranged to
satisfy: VH=-0.001X.sup.2+0.44X+125 VL=-0.0013X.sup.2+0.69X+160
where X expresses a distance between the nozzle and the discharge
target, and VH and VL express maximum and minimum values of
discharge start voltage at which discharge of the fluid from the
nozzle is started, respectively.
As with the aforementioned electrostatic suction type fluid
discharge device, this device also achieves both the
miniaturization of nozzle and the decrease in drive voltage.
Further, this structure in which the nozzle diameter is specified
in a range from .phi.1 .mu.m to .phi.5 .mu.m securely ensures the
effect of decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage at which the fluid is discharged from
the nozzle is set between the maximum value (VH) and the minimum
value (VL), which are specified as: VH=-0.001X.sup.2+0.44X+125 and
VL=-0.0013X.sup.2+0.69X+160, it is possible to perform stable and
reliable discharge of fluid from the nozzle in forming a micro
pattern.
Additional objects, features, and strengths of the present
invention will be made clear by the description below. Further, the
advantages of the present invention will be evident from the
following explanation in reference to the drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1(a) is a waveform diagram showing a waveform of pulse voltage
applied between a nozzle and a substrate, and transition in
meniscus surface potential, in an electrostatic suction type fluid
discharge device according to one embodiment of the present
invention.
FIG. 1(b) is a waveform diagram showing a waveform of pulse voltage
applied between a nozzle and a substrate, and transition in
meniscus surface potential, in a comparative example.
FIG. 2 is used for illustrating the calculation of the electric
field intensity in a discharge model that is a basic concept of the
present invention.
FIG. 3 is a graph showing a result of model calculation of
nozzle-diameter dependency of a surface tension pressure and
electrostatic pressure.
FIG. 4 is a graph showing a result of model calculation of nozzle
diameter dependency of a discharge pressure.
FIG. 5 is a graph showing a result of model calculation of nozzle
diameter dependency of a discharge limit voltage.
FIG. 6 shows a correlation between (i) an image force exerted
between an electrically charged droplet and a substrate and (ii)
the distance between a nozzle and the substrate.
FIG. 7 shows a result of model calculation of a correlation between
an applied voltage and the rate of fluid discharged from the
nozzle.
FIG. 8 is a graph showing the relationship among nozzle diameter,
discharge response, and discharge limit frequency.
FIG. 9 is an explanatory view including a cross section of lateral
side of major part of an electrostatic suction type fluid discharge
device according to one embodiment of the present invention.
FIG. 10(a) is a waveform diagram showing a waveform of pulse
voltage applied between a nozzle and a substrate, and transition in
meniscus surface potential.
FIG. 10(b) is a waveform diagram showing a waveform of pulse
voltage applied between a nozzle and a substrate, and transition in
meniscus surface potential.
FIG. 11 is a graph showing a result of test for discharge-start
response depending on the voltage value applied immediately before
a rise of pulse voltage applied between a nozzle and a
substrate.
FIG. 12(a) is a waveform diagram showing a waveform of pulse
voltage applied between a nozzle and a substrate, and transition in
meniscus surface potential.
FIG. 12(b) is a waveform diagram showing a waveform of pulse
voltage applied between a nozzle and a substrate, and transition in
meniscus surface potential.
FIG. 13 is a graph showing a result of test for discharge-start
response depending on the voltage value applied immediately before
a fall of pulse voltage applied between a nozzle and a
substrate.
FIG. 14 is a waveform diagram showing a waveform of pulse voltage
applied between a nozzle and a substrate, and transition in
meniscus surface potential.
FIG. 15(a) is a waveform diagram showing a (i) waveform at a start
of DC voltage application between a nozzle and a substrate, and
(ii) transition in meniscus surface potential, for an electrostatic
suction type fluid discharge device of FIG. 1.
FIG. 15(b) is a waveform diagram showing a (i) waveform at a start
of DC voltage application, and (ii) transition in meniscus surface
potential, for a comparative example.
FIG. 16(a) is a waveform diagram showing a (i) waveform at an end
of DC voltage application between a nozzle and a substrate, and
(ii) transition in meniscus surface potential, for an electrostatic
suction type fluid discharge device of FIG. 1. FIG. 16(b) is a
waveform diagram showing a (i) waveform at an end of DC voltage
application, and (ii) transition in meniscus surface potential, for
a comparative example.
FIG. 17 is an explanatory view showing a difference in drawing
pattern between low-speed driving and high-speed driving.
FIG. 18 is an explanatory view including a cross section of lateral
side of major part of an electrostatic suction type fluid discharge
device according to another embodiment of the present
invention.
FIG. 19 is an explanatory view showing a relative speed between a
discharge head and a substrate stage.
FIG. 20 is an explanatory view showing a relationship between (i) a
waveform of direct signal voltage applied between a nozzle and a
substrate and (ii) a period of intermittent discharge.
FIG. 21(a) is an explanatory view showing condition for drawing a
line with a single discharge pattern.
FIG. 21(b) is an explanatory view showing condition for drawing a
line with a single discharge pattern.
FIG. 21(c) is an explanatory view showing condition for drawing a
line with a single discharge pattern.
FIG. 22(a) is an explanatory view showing a relationship between
(i) a waveform of direct signal voltage applied between a nozzle
and a substrate and (ii) a period of intermittent discharge.
FIG. 22(b) is an explanatory view showing a relationship between
(i) a waveform of direct signal voltage applied between a nozzle
and a substrate and (ii) a frequency of intermittent discharge.
FIG. 23 is an explanatory view showing a relationship between (i) a
value of direct signal voltage applied between a nozzle and a
substrate and (ii) a frequency of intermittent discharge.
FIG. 24 is a graph showing a relationship between a scanning speed
and a minimum voltage to enable line-drawing.
FIG. 25(a) is a schematic structure view of an electrostatic
suction type fluid discharge device according to another embodiment
of the present invention.
FIG. 25 (b) is an equivalent circuit of the electrostatic suction
type fluid discharge device.
FIG. 26 is a graph showing a relationship between (i) an
application time of drive voltage and (ii) a discharge-start
voltage, for an electrostatic suction type fluid discharge device
of FIG. 25(a).
FIG. 27 (a) is a graph for showing change in meniscus surface
potential until it reaches the potential at which discharge is
started, for an electrostatic suction type fluid discharge device
of FIG. 25(a). In the graph, the application voltage and the
application time are set to 440V and 2400 .mu.sec,
respectively.
FIG. 27 (b) is a graph where the application voltage and the
application time are set to 680V and 1200 .mu.sec,
respectively.
FIG. 27 (c) is a graph where the application voltage and the
application time are set to 1600V and 400 .mu.sec,
respectively.
FIG. 28 is a waveform diagram showing an example of drive voltage
outputted from a power source shown in FIG. 25(a).
FIG. 29 is a graph showing a relationship between (i) a nozzle
diameter and (ii) a discharge-start voltage of material from a
nozzle, for an electrostatic suction type fluid discharge device of
FIG. 25(a).
FIG. 30 is a graph showing a relationship between (i) a
discharge-start voltage and (ii) a distance between the tip of
nozzle and a substrate, for an electrostatic suction type fluid
discharge device of FIG. 25(a). The figure shows respective cases
for plural nozzles having different diameters.
FIG. 31 is a graph showing a relationship between (i) an
application voltage to a drive electrode (drive voltage) and (ii)
variation in meniscus surface potential, for an electrostatic
suction type fluid discharge device of FIG. 25(a).
FIG. 32 illustrates the principle of the development of a
discharged fluid on account of electrostatic thread-like
phenomenon, in the electrostatic suction type fluid discharge
device.
BEST MODE FOR CARRYING OUT THE INVENTION
The following describes a concrete example and a comparative
example so as to more specifically explain the present invention.
The examples below are however not to limit the present
invention.
An electrostatic suction type fluid discharge device according to
the present embodiment has a nozzle with a diameter of 0.01 .mu.m
to 25 .mu.m, and can control the discharge of fluid to be
discharged with a drive voltage not more than 1000V.
In a conventional fluid discharge model, since a smaller nozzle
diameter requires a higher drive voltage, when the nozzle diameter
is not more than 50 .mu.m, ink is assumed not to be discharged by a
drive voltage not more than 1000V unless the device is specially
designed, for example, to apply back pressure. However, the
inventor of the present invention have devoted themselves to
reviewing, and found that a nozzle having a specific diameter or
less causes a discharge phenomenon in a discharge model which
differs from the conventional fluid discharge model. The present
invention is made based on this new fluid discharge model using a
local electric field.
First, the fluid discharge model using a local electric field is
explained below with reference to FIGS. 2 through 7.
Assuming that a conductive fluid is injected into a nozzle having a
diameter of d (this hereinafter indicates an internal diameter of
nozzle unless otherwise specified), and the nozzle is positioned at
a point of height h, vertically to an infinite flat plate
conductor. FIG. 2 shows this state. Q=2.pi..di-elect
cons..sub.0.alpha.V.sub.0d (5)
Here, the electric charge Q induced in the tip of nozzle (nozzle
hole), which is assumed to be gathered to a hemispherical section
formed by the fluid in the tip of nozzle, is expressed as
follows.
In the Formula (5), Q (C) expresses a charge induced in the tip of
nozzle, .di-elect cons..sub.0 expresses a dielectric constant (F/m)
of a vacuum, d expresses a nozzle diameter, V.sub.0 expresses a
gross voltage applied to the nozzle. Further, .alpha. expresses a
proportionality constant which relies on the shape of nozzle and
some other factors, a generally being about 1-1.5, and becomes
substantially 1 under condition: d<<h (h: distance (m)
between nozzle (nozzle hole, to be more specific) and
substrate.
Further, when the substrate is a conducting substrate, it would
appear that a mirror image charge Q' having a polarity opposite to
that of the charge Q is induced in a symmetrical and opposed
position to the nozzle on the substrate. Similarly, when the
substrate is an insulator, the image charge Q having a polarity
opposite to that of a video Q' is induced in a symmetric position
which is determined depending on the dielectric constant of the
substrate.
The intensity of gathered electric field E.sub.loc is figured out
by the following Formula (6), where R expresses a curvature radius
of the tip section of nozzle.
##EQU00005##
In the formula, k expresses a proportionality constant which relies
on the shape of nozzle and some other factors, k generally being
about 1.5-8.5, often being about 5 (P. J. Birdseye and D. A. Smith,
Surface Science, 23(1970), p. 198-210). Further, here, the
condition R=d/2 is set so as to make the structure of fluid
discharge model simple. This condition denotes a state that the
fluid in the tip of nozzle is extruded in a hemispherical shape,
whose curvature radius is equal to that of the nozzle diameter d,
by the surface tension.
Here, to look at the balance of pressure applied to the fluid in
the tip of nozzle, the electrostatic pressure P.sub.e is first
found as follows, where S expresses the area of liquid in the tip
of nozzle.
.times..times..pi..times..times..times. ##EQU00006##
Then, assuming a condition: .alpha.=1 according to the Formulas (5)
through (7), the pressure P.sub.e is further expressed as
follows.
.times..times..times..times..times. ##EQU00007##
Meanwhile, the pressure P.sub.s, which is caused by the surface
tension of the fluid in the tip of nozzle, is found as follows
where .gamma. expresses the surface tension.
.times..gamma. ##EQU00008##
To cause a fluid to be discharged, the electrostatic force needs to
be greater than the surface tension, and therefore the relationship
between the electrostatic pressure P.sub.e and the pressure P.sub.s
by the surface tension is found as follows. P.sub.e>P.sub.s
(10)
FIG. 3 shows a relationship between the electrostatic pressure
P.sub.e and the pressure P.sub.s by the surface tension for a
nozzle having a diameter=d. The surface tension is found by
assuming that the fluid is water (.gamma.=72 mN/m). On the
stipulation that the voltage applied to the nozzle is 700V, the
electrostatic pressure P.sub.s appears to be greater than the
pressure P.sub.s by the surface tension when the nozzle diameter d
is 25 .mu.m. According to this, the following Formula (11) denotes
the relationship between V.sub.0 and d at the minimum voltage to
cause the fluid to be discharged.
>.gamma..times..times..times. ##EQU00009##
Further, the discharge pressure .DELTA.P is given by the Formula
(12), and is finally given by the Formula (13).
.DELTA..times..times..DELTA..times..times..times..times..times..gamma.
##EQU00010##
FIG. 4 shows a dependency of the discharge pressure .DELTA.P when
the condition to cause discharge in a nozzle having a diameter=d is
met by a local electric field strength. FIG. 5 shows a dependency
of critical discharge voltage (minimum voltage to cause discharge)
Vc.
As can be seen in FIG. 4, if the condition to cause discharge in a
nozzle having a diameter=d is met by a local electric field
strength (when the condition: V.sub.0=700V, .gamma.=72 mN/m is
assumed), the upper limit of the nozzle diameter is 25 .mu.m.
In the calculation in FIG. 5, the condition: K=5 was satisfied by
assuming that the fluid is water (.gamma.=72 mN/m) and an organic
solvent (.gamma.=20 mN/m). In consideration of the effect that the
micro nozzle causes an electric field to be converged, this figure
clearly shows that the critical discharge voltage decreases as the
nozzle diameter decreases, and therefore the critical voltage to
discharge water is figured out as about 700V for a 25 .mu.m
nozzle.
In only the idea of electric field for the conventional discharge
model, that is an electric field defined by the voltage V.sub.0
applied to the nozzle and the distance h between the nozzle and the
counter electrode, is taken into account; the drive voltage to
cause discharge increases as the diameter of nozzle becomes
smaller.
However, in the discharge model using a local electric field for
which the local electric field strength is also taken into account,
the drive voltage for discharge can be reduced by a microscopic
size nozzle. Such reduction in drive voltage offers a great
advantage to miniaturize the device and to realize high-density
nozzle. Besides, decreasing the drive voltage also enables use of a
low voltage driver which appreciably helps cost reduction.
Moreover, in the discharge model using the local electric field,
the electric field strength required for discharge depends on the
converged local electric field strength, and therefore the counter
electrode can be omitted. More specifically, in a conventional
discharge model, an electric field is applied between the nozzle
and the substrate, and therefore it was necessary to either provide
a counter electrode on the other side of nozzle when using an
insulating substrate, or use a conducting substrate. Further, in
forming the counter electrode, that is, when the substrate is an
insulator, the thickness of the substrate was limited.
On the other hand, the discharge model using the local electric
field is capable of printing on an insulating substrate without
using a counter electrode, allowing more flexible device
arrangement. Further, it is capable of printing on a thick
insulator.
Further, since the fluid discharged from the nozzle is electrically
charged, an image force is generated between the fluid and the
substrate. FIG. 6 shows a correlation between the magnitude of the
image force and the distance h of nozzle from the substrate. As
shown therein, the image force becomes more significant as the
distance between the substrate and the nozzle decreases,
particularly when h becomes smaller than 20 .mu.m.
Next, the following assumption is made to find a way of precisely
controlling the discharge flow rate. For a viscid fluid, the flow
rate Q in a cylinder path is denoted by the following Hagen
Poiseuille Formula. When a cylinder nozzle is used, the flow rate Q
in the nozzle is expressed as follows.
.pi..times..times..DELTA..times..times..eta..times..times..times.
##EQU00011##
In the formula, .eta. expresses a viscosity coefficient (Pas), L
expresses a length (m) of flow path (nozzle), d expresses a
diameter (m) of flow path (nozzle hole), and .DELTA.P expresses a
pressure difference (Pa). The foregoing formula indicates that the
flow rate Q is proportional to the fourth power of the radius of
flow path, meaning that the flow rate can be effectively controlled
by using a micro nozzle. The value found by Formula (13) is used in
the Formula (14), and the following Formula (15) is obtained.
.times..pi..times..times..eta..times..times..times..times..times..gamma.
##EQU00012##
The Formula (15) is to find an amount of fluid flowing out of a
nozzle having a length=L and a diameter=d, when a voltage V is
applied to the nozzle. FIG. 7 shows this state. The amount is
calculated on condition that: L=10 mm, .eta.=1 (mPas), .gamma.=72
(mN/m). In this case, the diameter of nozzle is assumed to be 50
.mu.m, the minimum diameter among the conventional nozzles. The
voltage V is gradually applied, and the fluid is started to be
discharged at 1000V, which corresponds to the discharge-start
voltage mentioned in FIG. 5. The Y axis denotes the flow rate of
fluid from the nozzle. The flow rate jumps right after the
discharge-start voltage Vc.
According to this model calculation, a micro flow rate appears to
be obtained by precisely setting the voltage to a value slightly
above Vc. However, as can be seen in the semilog diagram, it is not
possible in actual operation, particularly for a tiny amount below
10.sup.-10 m.sup.3/s. Moreover, as explained above with Formula
(11), a minimum drive voltage for a nozzle having a certain
diameter is automatically determined. Therefore, discharging of
fluid less than 10.sup.-10 m.sup.3/s, or application of voltage
less than 1000V is not practically realistic as long as the nozzle
diameter is at least 50 .mu.m.
As can be seen in the diagram, a nozzle having a diameter=25 .mu.m
can easily discharge a minute amount of fluid with a drive voltage
of 700V or even less than that, and if the diameter is only 10
.mu.m, discharge of that can be controlled by a voltage less than
500V. Further, a nozzle of 1 .mu.m can be driven by a voltage less
than 300V.
The foregoing theory was presented with an assumption that the
fluid is discharged as a continuous flow. The following explains a
switching operation to discharge a one-shot flow.
The discharge by electrostatic absorption is based on charging of
fluid in the tip of nozzle. The charging speed is estimated at
around the time constant, which depends on the dielectric
relaxation.
.tau..sigma. ##EQU00013##
In the formula, .di-elect cons. expresses relative dielectric
constant, and .sigma. expresses conductivity of fluid (Sm).
Assuming that the relative dielectric constant is 10, and the
conductivity is 10.sup.-6 S/m, a condition:
.tau.=1.854.times.10.sup.-5 sec is found. Further, if the critical
frequency is denoted by fc, the Formula (17) is given.
.sigma. ##EQU00014##
Accordingly, it is not possible to follow a change in electric
field at a frequency higher than fc, that is, the discharge does
not occur. On this stipulation, a frequency for the case above is
estimated at about 10 kHz.
Next, the following takes up a decrease of surface tension in the
nozzle wall. Assuming a droplet of fluid discharged on an insulator
placed on an electrode, the contact area of the fluid and the
insulator can be increased by applying a voltage between the fluid
and the electrode, in other words, the voltage application improves
wettability. This phenomenon is known as Electrowetting. This
effect also works for a cylindrical capillary, in which case it is
often called Electrocapillary. The relation among (i) pressure due
to Electrowetting, (ii) applied voltage, (iii) shape of capillary,
and (iv) physicality value of solvent is denoted by the Formula
(18) below.
.times..times..times. ##EQU00015##
In the formula, .di-elect cons..sub.0 expresses dielectric constant
in a vacuum, .di-elect cons..sub.r expresses dielectric constant of
insulator, t expresses thickness of insulator, and d expresses
internal diameter of capillary. Adopting this formula with an
assumption that the fluid is water, the case described in "Example"
of the foregoing Japanese Examined Patent application Tokkosho
36-13768 (published on Aug. 18, 1961) was examined, with a result
of 30000 Pa (0.3 atm), which is not so significant. On the other
hand, the same examination was carried out for the present
invention with the result of about 30 atm when an electrode is
provided outside the nozzle. With this effect, the fluid is quickly
supplied to the tip of nozzle even in the case of micro nozzle.
This effect becomes more significant as the dielectric constant of
insulator increases, and as the thickness decreases. Strictly, the
electrode needs to be placed on an insulator to obtain
Electrocapillary; however, the effect can still be obtained as long
as sufficient electric field is applied to a sufficient
insulator.
However, it should be noted in presenting this approximate theory
that the strength of electric field in this case denotes not the
conventional sense of electric field which depends on the voltage
V.sub.0 applied to the nozzle and the distance h between the nozzle
and the counter electrode, but a strength of converged local
electric field in the tip of nozzle. Further, an important feature
of the present invention is the use of converged local electric
field, and a fluid-supplying path having a significantly small
conductance. Also, in the present invention, the fluid is
sufficiently charged even in a unit of micro area.
On this account, when a dielectric substance, such as a substrate,
or an electric conductor approaches, the small amount of fluid is
ejected at right angles with respect to the substrate due to the
image force. Considering this structure, a grass capillary is used
in the Embodiment below because of its simple fabrication; however,
the present invention is not limited to this.
[First Embodiment]
As described above, the nozzle diameter and the drive voltage are
both reduced in an electrostatic suction type fluid discharge
manner using a local electric field. However, when discharging a
one-shot flow of fluid, this method also carries out application of
pulse voltage between the nozzle filled with the fluid and the
substrate placed oppositely to the nozzle tip, attracting the
liquid in the nozzle end toward the substrate, so that a droplet is
formed on the substrate.
In this method, the amount of fluid discharged from the nozzle
increases as the upper-limit voltage (maximum value) of pulse
voltage, which is applied between the nozzle and the substrate,
increases; that is the amount decreases as the upper-limit voltage
of pulse voltage decreases. More specifically, the discharge amount
can be controlled by controlling the maximum value of pulse
voltage.
However, in this model, the discharge response is basically
determined by (i) an electric resistance R of the fluid residing
between the electrode inside the nozzle and the nozzle tip and (ii)
a time constant RC, that is a product of electrostatic capacitance
C between the meniscus in the nozzle tip and the substrate.
Further, the parameters for determining the electric resistance R
and the electrostatic capacitance C include the nozzle diameter d.
That is, the discharge response depends on the nozzle diameter
d.
FIG. 8 is a graph showing a discharge response of silver nano
paste. As can be seen in the figure, the time constant RC extremely
increases as the nozzle diameter decreases. This makes the
discharge response decrease, and also decreases the frequency limit
to cause discharge.
More specifically, in an electrostatic suction type fluid discharge
method by the fluid discharge model using a local electric field,
the discharge response extremely decreases as discharge amount
becomes very low, which gives another problem, a difficulty in
performing high-frequency driving. By increasing the upper-limit
voltage of the pulse voltage applied between the nozzle and the
substrate, the discharge response certainly increases, enabling the
driving to be carried out at relatively high-frequencies. However,
this structure requires a high-voltage driver for applying a
high-voltage to the driving electrode. Because of this, the cost
reduction due to the use of low-voltage driver, which was the main
advantage of an electrostatic suction type fluid discharge method
by a fluid discharge model using a local electric field, cannot be
attained.
To be more specific, the discharge response is broken into a
discharge-start response at a rise of pulse voltage, and a
discharge-end response at a fall of pulse voltage. In view of this,
a low discharge response automatically means incapability of
control of discharge amount accurately in response to the
application time of the upper-limit voltage.
Besides, such a problem of response at a rise/fall of voltage
affects not only application of the pulse voltage but also
application of DC voltage when actually drawing a line on the
substrate. That is, the decrease in discharge-start response at the
beginning of DC voltage application also decreases accuracy of
control for the start-position of discharge, which is supposed to
depend on the start-position of application of DC voltage.
Similarly, the decrease in discharge-end response at the end of DC
voltage application also decreases accuracy of control for the
end-position of discharge, which is supposed to depend on the
end-position of application of DC voltage.
Because the electrostatic suction type fluid discharge method by a
fluid discharge model using a local electric field allows discharge
of much less amount of fluid than the that discharged in the
conventional device, the dot diameter, the dot pitch, the width,
pitch, or length of line (in the case of line drawing) all have
become finer. This is why the foregoing new problems have
arisen.
The electrostatic suction type fluid discharge device according to
the present invention has a specific arrangement of the waveform of
voltage applied between the nozzle and the substrate. With this
arrangement, the device is driven at high-frequencies by a cost
favorable low-voltage driver, while ensuring accuracies in control
of discharge amount which depends on the application time of the
upper-limit voltage and in control for the start/end-position of
discharge which depends on the start/end-timing of application of
DC voltage. The following more specifically explains the structure
of this electrostatic suction type fluid discharge device.
FIG. 9 is a cross section of lateral side of an electrostatic
suction type fluid discharge device according to one embodiment of
the present invention. The reference numeral 1 in the figure
indicates a nozzle having a super-micro diameter. At the tip of the
nozzle is formed a nozzle hole (discharge hole) having a
super-micro diameter. In order to realize discharge of very few
amount of fluid, it is necessary to either dispose a
low-conductance flow path in the neighborhood of the nozzle 1 or
adopt a low-conductance nozzle 1. For this reason, a glass
capillary is suitable, but conductive material coated by insulating
material is also applicable.
The followings are typical advantages of a glass nozzle. Firstly,
it is easy to form a nozzle hole of several .mu.m on a glass
nozzle. Secondly, in the case of blockage of nozzle, it is easy to
reproduce another nozzle end by breaking the old nozzle end.
Thirdly, its taper angle makes unnecessary solvent move upward (an
opposite side to the nozzle hole side in a case where the nozzle 1
is so disposed that the nozzle hole is positioned at the lower end)
by surface tension, so that the unnecessary solvent would not be
accumulated in the nozzle end, and therefore does not cause
blockage of nozzle. Finally, the glass nozzle 1 is moderately
flexible, and therefore may serve as a movable nozzle.
More specifically, the nozzle 1 can be formed from a glass
capillary with filament (product name: GD-1 manufactured by
Narishige Co. Ltd.) by using a capillary puller. The followings are
advantages of using the glass capillary with filament.
(1) It is easy to fill the nozzle with ink because the glass on the
filament side is easily soaked by the ink; (2) because the glass on
the filament side is hydrophilic whereas that on the external side
is hydrophobic, the ink stays in a limited space, that
substantially corresponds to the inner diameter of the glass on the
filament side at the tip of the nozzle, by which the intensive
electric field becomes further significant; (3) it becomes possible
to miniaturize the nozzle; and (4) sufficient mechanical intensity
can be obtained.
It is preferable that the lower limit value of the diameter of the
nozzle hole (hereinafter, the diameter will be referred to as a
nozzle diameter) be 0.01 .mu.m, in consideration of production
convenience. Further, it is preferable that the upper limit value
of the nozzle diameter be 25 .mu.m, or more preferably 15 .mu.m,
because (i) the upper limit of the nozzle diameter in the case
where the electrostatic force exceeds the surface tension, as shown
in FIG. 3, is 25 .mu.m, and (ii) the upper limit of the nozzle
diameter in the case where the discharge condition is satisfied on
an account of local electric field intensity, as shown in FIG. 4,
is 25 .mu.m. Especially, in order to more effectively utilize the
local electric field intensity, it is preferable that the nozzle
diameter be in a range of 0.01 .mu.m to 8 .mu.m.
Further, the nozzle 1 is not limited to the capillary tube, and it
may be a two-dimensional pattern nozzle formed by minute
processing. In a case where the nozzle 1 is made of glass that is
easy to be formed, the nozzle 1 cannot function as an electrode.
Therefore, an electrode 2 (described later) of metal wire (for
example, a tungsten wire) is inserted into the nozzle 1. The
electrode 2 may be formed inside the nozzle 1 by plating. In a case
where the nozzle 1 is made of conductive material, insulating
material is applied thereon.
A discharge material 3 is supplied into the nozzle 1 from a fluid
supply source (not illustrated) until it fills up the nozzle 1. The
discharge material 3 is an object to be discharged from the nozzle
1 via a supply path 8. Further, the electrode 2 is so disposed in
the nozzle 1 as to be soaked in the discharge material 3. The
nozzle 1 is mounted to the holder 6 by a shield rubber 4 and a
nozzle clamp 5.
With the effect of converged electric field at the tip of the
nozzle, and the effect of the image force exerted on the counter
substrate, the present invention allows omission of counter
substrate, which is supposed to be provided at a rear side of the
substrate, or a conductive substrate, which were required in the
conventional discharge device. Therefore, an insulating glass
substrate, a plastic substrate such as polyimide, a ceramics
substrate, a semiconductor substrate or other types of substrate
can be used as the substrate.
However, in order to ensure stable landing of the discharge
material 3 from the nozzle hole of the nozzle 1 onto the surface of
the substrate 13, the present embodiment uses a counter electrode
14, which is provided to be opposed to the nozzle hole of the
nozzle 1 with a certain distance therefrom. The substrate 13 is
disposed between the counter electrode 14 and the nozzle 1.
The electrode 2 and the counter electrode 14 are connected to the
voltage applying section 9. The voltage applying section 9 controls
at least one of the voltages applied to the electrode 2 or that
applied to the counter electrode 14, so as to apply the pulse
voltage for a one-shot flow discharge, or a direct current bias
voltage for a continuous discharge of fluids, between the tip of
the nozzle 1 and the substrate 13. A positive or negative voltage
may be arbitrarily used for this voltage applied between the tip of
the nozzle 1 and the substrate 13.
Before explaining application of voltage by the voltage applying
section 9, the following shows the result of discharge response
test, in which various voltages are applied between the nozzle 1
and the substrate 13, and the discharge response is checked for
each case.
First of all, the pulse voltages shown in FIGS. 10(a) and 10(b) are
applied between the nozzle 1 and the substrate 13.
For the pulse voltages shown in FIGS. 10(a) and 10(b), their upper
limit voltages 10 are set to the same voltage that is equal to or
greater than the minimum discharge-inducing voltage 30. The period
and the cycle of applying the upper voltages 10 are the same, but
their lower limit voltages 20 are different. The lower limit
voltage 20 of FIG. 10(b) is set to 0V, whereas the lower limit
voltage 20 of FIG. 10(a) is set greater than 0V and lower than the
minimum discharge-inducing voltage 30.
The minimum discharge-inducing voltage 30 designates the required
voltage condition to cause discharge in the case where the fluid is
discharged by application of direct current bias. Discharge starts
when the meniscus surface potential formed of the fluid at the tip
of the nozzle 1 (nozzle hole) reaches the minimum
discharge-inducing voltage 30. For example, when the tip diameter
of the nozzle is 2 .mu.m, the minimum discharge-inducing voltage 30
is approximately 150V.
The present embodiment describes an exemplary case where the upper
limit voltage 10 has a positive polarity. However, as described
above, the upper limit voltage 10 may have a negative polarity.
Therefore, the level of the voltage used in the description
corresponds to the amount of the absolute value, which is measured
from a reference value=0V.
When the pulse voltages having such waveforms are applied, a
relationship between the discharge condition and the change of the
meniscus surface potential at the tip of the nozzle 1 can be
described as follows. In the pulse voltage shown in FIG. 10(b), the
lower limit voltage 20 is set to 0V, and therefore, discharge
material 3 becomes conducted immediately after the pulse voltage is
applied. Then, electric charge is accumulated in the meniscus at
the tip of the nozzle 1, and the meniscus surface potential
(indicated by a broken line in the figures) 40 increases. The
increase of the meniscus surface potential 40 normally draw a
saturation curve although it may differ depending upon the electric
conductivity of the upper limit voltage 10 or the discharge
material 3, and the resistance of the fluid path in the nozzle 1.
Discharge starts when the meniscus surface potential 40 reaches the
minimum discharge-inducing voltage (indicated by a dot line in the
figures) 30. However, in the case of FIG. 10(b), the meniscus
surface potential 40 does not reach the minimum discharge-inducing
voltage 30 within the application time of the upper limit voltage
10. Therefore, no discharge occurs. After the fall of the upper
limit voltage 10, the accumulated electric charge in the meniscus
starts to be electrically discharged correspondingly to the
potential difference to the lower limit voltage 20, and the
meniscus surface potential 40 is attenuated. Therefore, in the
comparative example, increase and attenuation of the meniscus
surface potential 40 alternately happen according to the pulse
voltage period, and the discharge of fluid does not occur.
On the other hand, in the pulse voltage in FIG. 10(a), the lower
limit voltage 20 is set greater than 0V. Therefore, electric charge
is previously accumulated on the meniscus before the upper limit
voltage 10 is applied, and the meniscus surface potential 40 is
approximately the same as the lower limit voltage 20. As the upper
limit voltage 10 is applied (risen), the meniscus surface potential
40 starts increasing, starting from the same value as the lower
limit voltage 20. The meniscus surface potential 40 reaches the
minimum discharge-inducing voltage 30 within the application time
of the upper limit voltage 10. When the meniscus surface potential
40 reaches the minimum discharge-inducing voltage 30, discharge of
the fluid starts. After the fall of the upper limit voltage 10, the
discharge ends concurrently with the attenuation of the meniscus
surface potential 40.
As described above, by previously applying a bias having the same
polarity as that of the upper limit voltage 10 as the lower limit
voltage 20, the meniscus surface potential 40 reaches the minimum
discharge-inducing voltage 30 by the upper limit voltage 10 within
the application time with which the discharge of fluid does not
occurs when the lower limit voltage 20 was 0V, thereby causing the
fluid to be discharged. Therefore, the fluid can be discharged
according to the pulse voltage period (period of the upper limit
voltage).
As the time taken to start discharge since the upper limit voltage
10 rises is shortened, more immediate discharge-start response is
obtained. Therefore, if only the discharge-start response is taken
into consideration, the lower limit voltage 20 is preferably set to
the same polarity as that of the upper limit voltage 10, however to
a lower value than that of the minimum discharge-inducing voltage
30. Within this range, the lower limit voltage 20 is preferably set
as high as possible, that is, as close to the minimum
discharge-inducing voltage 30 as possible.
FIG. 11 shows a result of test for discharge-start response, using
the silver nano paste manufactured by HARIMA CHEMICALS, INC (with
the nozzle diameter of 12 .mu.m). In order to confirm the discharge
characteristics in conformity with the electric conductivity of the
silver nano paste, the upper limit voltage 10 of the pulse voltage
was set to +450V, and the application time of the upper limit
voltage 10 was set to 2000 .mu.sec. In this experiment, the minimum
discharge-inducing voltage 30 was +200V.
As shown in FIG. 11, as the lower limit voltage 20 of the pulse
voltage was increased from 0V to +150V, the time taken to start
discharge since the upper limit voltage 10 was applied gradually
decreases. This proved the effect on the improvement in the
discharge response by the use of the lower limit voltage 20.
This indicates that the discharge-start response can be improved by
the lower limit voltage 20 having the same polarity as that of the
upper limit voltage 10 and lower than the minimum
discharge-inducing voltage 30. As a result, the drive frequency
increases.
Subsequently, the pulse voltages shown in FIGS. 12(a) and 12(b) are
applied between the nozzle 1 and the substrate 13.
For the pulse voltages shown in FIGS. 12(a) and 12(b), their upper
limit voltages 10 are set to the same voltage that is equal to or
greater than the minimum discharge-inducing voltage 30. Their
application times and periods of the upper voltages 10 are also the
same, but the lower limit voltages 20 have different values. The
lower limit voltage 20 of FIG. 12(b) has the same polarity as that
of the upper limit voltage 10, whereas the lower limit voltage 20
in FIG. 12(a) has the opposite polarity to that of the upper limit
voltage 10.
When the pulse voltages having such waveforms are applied, the
relationship between discharge and change in the meniscus surface
potential 40 at the tip of the nozzle 1 becomes as follows. In the
comparative example shown in FIG. 12(b), the lower limit voltage 20
and the upper limit voltage 10 have the same polarity. Therefore,
the potential difference between the lower limit voltage 20 and the
meniscus surface potential 40 after the fall of the upper limit
voltage 10 is small, and an attenuation speed of the meniscus
surface potential 40 after the fall of the upper limit voltage 10
is slow. Consequently, it takes a while for the meniscus surface
potential 40 to reach the minimum discharge-maintaining voltage
(indicated by a dot line in the figures) 50 after the fall of the
upper limit voltage 10, and therefore the discharge continues for a
while. FIG. 12(b) shows the most extreme case thereof. Because the
lower limit voltage 20 is extremely high, the meniscus surface
potential 40 does not fall below the minimum discharge-maintaining
voltage 50 within the application period of the lower limit voltage
20. Therefore, intermittent discharge continuously happens in the
entire pulse signal period (application period of the upper limit
voltage).
On the other hand, in the pulse voltage according to the present
embodiment that is shown in FIG. 12(a), the lower limit voltage 20
and the upper limit voltage 10 have opposite polarities. Therefore,
the potential difference between the lower limit voltage 20 and the
meniscus surface potential 40 after the fall of the upper limit
voltage is large, and the attenuation speed of the meniscus surface
potential 40 is fast. This expedites the timing where the meniscus
surface potential 40 becomes lower than the minimum
discharge-maintaining voltage 50 due to attenuation, thereby
improving separation of fluids. As a result the discharge-end
response improves.
As described above, by setting the lower limit voltage 20 to the
opposite polarity to that of the upper limit voltage 10 and
applying an opposite polarity bias after the fall of the upper
limit voltage 10, termination of discharge after the fall of the
upper limit voltage 10 is facilitated, thus improving the
discharge-end response. By improving the discharge-end response,
discharge limit frequency is also improved.
As the time taken to end discharge since the upper limit voltage 10
falls is shortened, more immediate discharge-end response is
obtained Therefore, if only the discharge-end response is taken
into consideration, the lower limit voltage 20 should be set to a
maximally great value in the opposite polarity to that of the upper
limit voltage 10. However, if the absolute value exceeds the
absolute value of the minimum discharge-inducing voltage 30, the
meniscus surface potential 40 may turn into the opposite polarity,
although it depends upon the proportion of the application time of
the upper limit voltage 10 to that of the lower limit voltage 20
(duty ratio). Therefore, it is preferable that the absolute value
be set equal to or lower than the minimum discharge-inducing
voltage 30.
FIG. 13 shows a result of test for discharge-start response, using
the silver nano paste manufactured by HARIMA CHEMICALS, INC (with
the nozzle diameter of 12 .mu.m). In order to confirm the discharge
characteristics in conformity with the electric conductivity of the
silver nano paste, the upper limit voltage 10 of the pulse voltage
was set to +450V, and the application time of the upper limit
voltage 10 was set to 3000 .mu.sec. In this experiment, the minimum
discharge-inducing voltage 30 was +200V.
As shown in FIG. 13, as the lower limit voltage 20 of the pulse
voltage was increased from 0V to -200V, the time taken to start
discharge since the upper limit voltage 10 was applied gradually
decreases. This proves that the discharge response is improved by
setting the polarity of the lower limit voltage 20 to the opposite
polarity to that of the upper limit voltage 10.
The foregoing experiment shows that the discharge-end response can
be improved by setting the lower limit voltage 20 to the opposite
polarity to that of the upper limit voltage 10, thereby improving
drive frequency.
In view of the foregoing effect of improvement in the
discharge-start response and the discharge-end response by the
specific setting of lower limit voltage 20 of the pulse voltage,
the voltage applied between the nozzle 1 and the substrate 13 by
the voltage applying section 9 of the electrostatic suction type
fluid discharge device is set as follows.
FIG. 1(a) shows a waveform of pulse voltage applied between the
nozzle 1 and the substrate 13 by the voltage applying section 9, in
the case of droplets discharge. FIG. 1(b) shows a waveform in a
comparative example.
In the pulse voltage of the present embodiment and that of the
comparative example, the upper limit voltages 10 are set to the
same value that is equal to or greater than the minimum
discharge-inducing voltage 30. The application time and period of
the respective upper limit voltages 10 are also the same, but there
is a difference in the lower limit voltage 20. In the comparative
example, the lower limit voltage 20 is set to 0V. On the other
hand, in the present embodiment, the lower limit voltage 20 is so
set as to have two specific stages. To ensure the desired
discharge-start response, a first lower limit voltage (pre-charge
voltage) 20a is set immediately before the rise of the upper limit
voltage 10. The first lower limit voltage 20a has the same polarity
as that of the upper limit voltage 10, and is lower than the
minimum discharge-inducing voltage 30. To ensure the desired
discharge-end response, a second lower limit voltage (attenuation
facilitating voltage) 20b is set immediately after the fall of the
upper limit voltage 10. The second lower limit voltage has the
opposite polarity to that of the upper limit voltage 10.
When the pulse voltages having such waveform are applied, the
relationship between discharge and change of the meniscus surface
potential 40 at the tip of the nozzle 1 becomes as follows. In the
comparative example shown in FIG. 1(b), the lower limit voltage 20
is 0V. Therefore, the discharge material 3 becomes conducted
immediately after application of pulse voltage. Then, the meniscus
at the tip of the nozzle 1 starts to be electrically charged, and
the meniscus surface potential 40 increases. Eventually discharge
starts when the meniscus surface potential 40 reaches the minimum
discharge-inducing voltage 30. After the upper limit voltage 10
falls, and the meniscus surface potential 40 is attenuated, the
meniscus surface potential 40 starts decreasing and finally falls
below the minimum discharge-maintaining voltage 50, and the
discharge ends.
On the other hand, in the pulse voltage of the present embodiment
shown in FIG. 1(a), the first lower limit voltage 20a is set lower
than the minimum discharge-inducing voltage 30 immediately before
the rise of the upper limit voltage 10. Therefore, electric charge
is accumulated on the meniscus surface according to the first lower
limit voltage 20a. As a result, the meniscus surface potential 40
becomes approximately the same potential as the first lower limit
voltage 20a. Further, when the upper limit voltage 10 that is equal
to or greater than the minimum discharge-inducing voltage 30 is
applied, the meniscus surface potential 40 immediately reaches the
minimum discharge-inducing voltage 30, and discharge starts. On the
other hand, the second lower limit voltage 20b is set immediately
after the fall of the upper limit voltage 10, which second lower
limit voltage 20b has the opposite polarity to that of the upper
limit voltage 10. Therefore, the meniscus surface potential 40 is
attenuated rapidly after the fall of the upper limit voltage 10.
Consequently, the meniscus surface potential 40 immediately falls
below the minimum discharge-maintaining voltage 50, and the
discharge ends.
With the above structure, the discharge response can be improved
both at the rise and the fall of the upper limit voltage 10,
improving the discharge limit frequency. Further, by improving the
discharge response both at the rise and the fall of the upper limit
voltage 10, the discharge can be controlled according to the
application time of the upper limit voltage, allowing the amount of
discharge to be controlled according to time.
FIG. 14 shows a waveform of pulse voltage of a modified example
that is applied between the nozzle 1 and the substrate 13 by the
voltage applying section 9, in the case of the one-shot flow
discharge. The difference between the pulse voltage shown in FIG.
14 and that in FIG. 1(a) is the second lower limit voltage 20b
which is set immediately after the fall of the upper limit voltage
10. Here, the second lower limit voltage 20b is lower than the
first lower limit voltage 20a, and has the same polarity as that of
the upper limit voltage 10. If the second lower limit voltage 20b
has the same polarity, the closer to 0V the second lower limit
voltage 20b is, the better the discharge-end response is. Further,
the second lower limit voltage 20b may be a pulse voltage of 0V.
This, in comparison with the second lower limit voltage 20b having
the opposite polarity, is less effective for improving the
discharge-end response, but enables the one-shot flow discharge
with minimum no-discharge period, and therefore is effective for
formation of contiguous dots. Further, it becomes possible to adopt
a low-voltage driver because the potential difference between the
upper limit voltage and the lower limit voltage of the pulse
voltage becomes small.
FIG. 15(a) shows a waveform of rising DC voltage applied between
the nozzle 1 and the substrate 13 by the voltage applying section
9, in discharge of the continuous fluids. FIG. 15(b) shows a
waveform of rising DC voltage of the comparative example.
In FIG. 15(a), the bias voltage (pre-charge voltage) 25 is applied
immediately before the rise of the DC voltage 15. The bias voltage
25 has the same polarity as that of the DC voltage 15 and is lower
than the minimum discharge-inducing voltage 30. On the other hand,
in FIG. 15(b) of the comparative example, no bias voltage 25 is
applied, and therefore the DC voltage 15 rises from 0V.
In FIG. 15(b), the meniscus surface potential 40 starts increasing
from 0V after the rise of the DC voltage 15 because no bias voltage
25 is applied before the rise of the DC voltage. Therefore, it
takes a while for the meniscus surface potential 40 to reach the
minimum discharge-inducing voltage 30 by which the discharge is
induced, and thus it is not possible to start the discharge
directly in response to application of the DC voltage 15.
On the other hand, in FIG. 15(a), the bias voltage 25 is applied
immediately before the rise of the DC voltage 15. Therefore, the
meniscus surface potential 40 is previously increased to
approximately the same potential as that of the bias voltage 25.
Accordingly, the meniscus surface potential 40 reaches the minimum
discharge-inducing voltage 30 shortly after the DC voltage 15, and
thus the discharge is started approximately at the same time as
that the DC voltage 15 is applied. With regard to the
discharge-start response, the greater the bias voltage 25
immediately before the rise is within the range lower than the
minimum discharge-inducing voltage 30 is, the better the
discharge-start response is. In other words, the closer the bias
voltage 25 is to the minimum discharge-inducing voltage 30, the
better the discharge-start response is.
FIG. 16(a) shows a waveform of fall of the DC voltage applied
between the nozzle 1 and the substrate 13 by the voltage applying
section 9, in discharge of continuous fluids. FIG. 16(b) shows a
waveform of fall of the DC voltage of the comparative example.
In FIG. 16(a), the bias voltage (attenuation facilitating voltage)
26 is applied immediately after the fall of the DC voltage 15. The
bias voltage has the opposite polarity to that of the DC voltage
15. On the other hand, in FIG. 16(b) of the comparative example, no
bias voltage 26 is applied, and the DC voltage 15 falls to 0V.
In FIG. 16(b), no bias voltage 26 is applied after the fall of the
DC voltage, and the DC voltage 15 falls to 0V. Therefore, the
meniscus surface potential 40 forms a gradual attenuation curve.
Thus, it takes a while for the meniscus surface potential 40 to
become lower than the minimum discharge-maintaining voltage 50 by
which the discharge ends. Therefore, the end of discharge does not
directly correspond to the end of application of the DC
voltage.
On the other hand, in FIG. 16(a), the bias voltage 26 having the
opposite polarity is applied immediately after the fall of the DC
voltage 15. Therefore, compared to the case of FIG. 16(b), there is
a greater potential difference between the direct current 15 and
the meniscus surface potential 40 after the fall of the DC voltage
15, and the meniscus surface potential 40 forms a sharp attenuation
curve after the fall of the DC voltage 15. Thus, the meniscus
surface potential 40 soon becomes lower than the minimum
discharge-maintaining voltage 50, and the discharge ends
accordingly. This makes it possible to end the discharge
approximately in response to end of application of the direct
current bias. The discharge-end response improves when the bias
voltage 26 immediately after the fall has the opposite polarity to
that of the DC voltage 15, and the improvement becomes more
significant as the absolute value of the bias voltage 26 becomes
greater. However, if the absolute value exceeds that of the minimum
discharge-inducing voltage 30, the meniscus surface potential 40
may become greater on the opposite polarity side than the minimum
discharge-inducing voltage 30, depending upon the application time
of the bias voltage 26. This may induce discharge of fluid, as the
fluid is charged to the opposite polarity. Therefore, it is
preferable that the absolute value be set smaller than that of the
minimum discharge-inducing voltage 30.
The above structure achieves improvement of the discharge response,
that is, improvement for both of the discharge-start response and
the discharge-end response at the rise and the fall of the DC
voltage 15. Further, the precision of the discharge-start position
and the discharge-end position can be improved when line-drawing is
induced by the DC voltage 15.
Although the counter electrode 14 is used in the present
embodiment, as described above the counter electrode 14 is not an
indispensable component in the electrostatic suction type fluid
discharge structure according to the present invention. Therefore,
the pulse voltage shown in FIG. 1(a) may be generated only by the
voltage applied to the electrode 2 in the nozzle 1. As well as
this, the counter electrode 14 may be grounded, and the voltage
applying section 9 may control only the voltage applied to the
electrode 2 in the nozzle 1 in generating the pulse voltage shown
in FIG. 1(a).
Further, in the present embodiment, the rectangular pulses shown in
FIGS. 1, 10, 12, and 14-16 are presented as exemplary waveforms of
the pulse voltage applied between the tip of the nozzle 1 and the
substrate 13. However, these rectangular waves may instead be a
waveform with a low slew rate, such as a sine wave.
The present embodiment has been described as a most preferred
structure for achieving improvement for both of the discharge-start
response and the discharge-end response. However, as it is apparent
from the description with reference to FIGS. 10 to 13, the
discharge-start response and the discharge-end response are
independent from each other.
As described above, an electrostatic suction type fluid discharge
device according to the present invention, which device discharges
by electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, is characterized in that the
fluid discharge hole, provided in the nozzle, has a diameter
ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic suction type
fluid discharge device comprises voltage applying means for
applying a pulse voltage between the nozzle and the substrate, an
upper limit voltage of the pulse voltage being equal to or greater
than a minimum discharge-inducing voltage, that is a voltage
required to start discharge of the fluid, and a pre-charge voltage
is provided immediately before a rise of the pulse voltage, the
pre-charge voltage having a same polarity as that of the upper
limit voltage, an absolute value of the pre-charge voltage being
set smaller than the minimum discharge-inducing voltage.
With the above structure, the fluid discharge hole provided in the
nozzle has a diameter ranging from 0.01 .mu.m to 25 .mu.m, so that,
in accordance with the discharge model using a local electric
field, a local electric field is generated. Consequently, this
miniaturization of nozzle allows reduction in drive voltage for
discharge. Such reduction of the drive voltage is greatly
beneficial to realize miniaturization of the device while ensuring
high density. It may be obvious but reduction of the drive voltage
allows the use of a low-voltage driver that offers advantageous
cost performance.
Moreover, in the discharge model using the local electric field,
the electric field strength required for discharge depends upon the
converged local electric field strength, and therefore the counter
electrode can be omitted. In other words, it becomes possible to
carry out printing on an insulating substrate without using a
counter electrode, allowing more flexible device arrangement.
Further, it also becomes possible to print on a thick
insulator.
However, the miniaturization of the nozzle described above has such
a problem that, when the discharge amount becomes significantly
small, the discharge response suddenly slows down exponentially.
This makes the high-frequency drive difficult. By increasing the
upper-limit voltage of the pulse voltage applied between the nozzle
and the substrate, the discharge response increases to a certain
degree, allowing the driving to be carried out at relatively
high-frequencies. However, this structure requires a high-voltage
driver for applying a high-voltage to the driving electrode.
Because of this, the cost reduction due to the use of low-voltage
driver, which was the main advantage of the miniaturization of the
nozzle, cannot be attained.
When looking at the discharge response more specifically, it can be
divided into the discharge-start response at the rise of the pulse
voltage and the discharge-end response at the fall thereof.
Therefore, low discharge response implies incapability of control
of discharge amount with high accuracy, precisely dependent upon
the application time of the upper limit voltage.
On the other hand, in the above structure in which the voltage
applying means applies a pulse voltage between the nozzle and the
substrate, and an upper limit voltage of the pulse voltage is set
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid; a pre-charge
voltage is applied immediately before a rise of the pulse voltage,
the pre-charge voltage having a same polarity as that of the upper
limit voltage, an absolute value of the pre-charge voltage being
set smaller than the minimum discharge-inducing voltage. Therefore,
the meniscus surface potential is precharged to a certain degree in
advance before the rise of pulse voltage.
Therefore, after the rise of the pulse voltage, the meniscus
surface potential soon reaches the minimum discharge-inducing
voltage, that is a voltage required to induce discharge, and the
discharge starts. Therefore, discharge-start response can be
improved. Consequently, the discharge limit frequency can be
improved, making the high-frequency driving possible.
In order to achieve the above object, an electrostatic suction type
fluid discharge device according to the present invention, which
device discharges by electrostatic suction a fluid, which is
electrically charged by voltage application, from a fluid discharge
hole of a nozzle onto a substrate opposite to the nozzle, is
characterized in that the fluid discharge hole, provided in the
nozzle, has a diameter ranging from 0.01 .mu.m to 25 .mu.m, the
electrostatic suction type fluid discharge device comprises voltage
applying means for applying a pulse voltage between the nozzle and
the substrate, an upper limit voltage of the pulse voltage being
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid, and an
attenuation facilitating voltage is provided immediately after a
fall of the pulse voltage, the attenuation facilitating voltage
having an opposite polarity to that of the upper limit voltage.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, so
that the drive voltage can be reduced. This is greatly beneficial
to miniaturization of the device while ensuring high density, and
therefore the same above-described effects as that of the
electrostatic suction type fluid discharge device according to the
present invention is obtained. For example, it allows the use of a
low-voltage driver that offers advantageous cost performance.
Further, in the above structure in which the voltage applying means
applies a pulse voltage between the nozzle and the substrate, and
an upper limit voltage of the pulse voltage is set equal to or
greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid, and an
attenuation facilitating voltage is provided immediately after a
fall of the pulse voltage, the attenuation facilitating voltage
having an opposite polarity to that of the upper limit voltage.
Therefore, the meniscus surface potential is rapidly attenuated
after the fall of the pulse voltage.
Therefore, after the fall of the pulse voltage, the meniscus
surface potential soon becomes lower than the minimum
discharge-maintaining voltage, that is a voltage required to
maintain discharge, and the discharge stops. Therefore,
discharge-end response can be improved. Consequently, the discharge
limit frequency can be improved, making the high-frequency driving
possible.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, wherein the fluid discharge hole,
provided in the nozzle, has a diameter ranging from 0.01 .mu.m to
25 .mu.m, the electrostatic suction type fluid discharge device
comprises voltage applying means for applying a pulse voltage
between the nozzle and the substrate, an upper limit voltage of the
pulse voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid, a pre-charge voltage is provided
immediately before a rise of the pulse voltage, the pre-charge
voltage having a same polarity as that of the upper limit voltage,
an absolute value of the pre-charge voltage being set smaller than
the minimum discharge-inducing voltage, and an attenuation
facilitating voltage is provided immediately after a fall of the
pulse voltage, the pre-charge voltage having an opposite polarity
to that of the upper limit voltage.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m,
and therefore the drive voltage can be reduced. This is greatly
beneficial to miniaturization of the device while ensuring high
density, and therefore the same above-described effects as that of
the electrostatic suction type fluid discharge device according to
the present invention is obtained. For example, it allows the use
of a low-voltage driver that offers advantageous cost
performance.
Further, in the above structure in which the voltage applying means
applies a pulse voltage between the nozzle and the substrate, and
an upper limit voltage of the pulse voltage is set equal to or
greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid; a pre-charge
voltage is provided immediately before a rise of the pulse voltage,
the pre-charge voltage having a same polarity as that of the upper
limit voltage, an absolute value of the pre-charge voltage being
set smaller than the minimum discharge-inducing voltage, and an
attenuation facilitating voltage is provided immediately after the
fall of the pulse voltage, the pre-charge voltage having an
opposite polarity to that of the upper limit voltage.
Therefore, as described above, the discharge-start response and the
discharge-end response can be simultaneously improved.
Consequently, the discharge limit frequency is more effectively
improved, making further high-frequency driving possible. Moreover,
because the discharge can be controlled in such a way as to be
dependent on the application time of the upper limit voltage, it
also becomes possible to so control the amount of discharge as to
be dependent on the time.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, wherein the fluid discharge hole,
provided in the nozzle, has a diameter ranging from 0.01 .mu.m to
25 .mu.m, the electrostatic suction type fluid discharge device
comprises voltage applying means for applying a pulse voltage
between the nozzle and the substrate; an upper limit voltage of the
pulse voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid; a pre-charge voltage is provided
immediately before a rise of the pulse voltage, the pre-charge
voltage having a same polarity as that of the upper limit voltage,
an absolute value of the pre-charge voltage being set smaller than
the minimum discharge-inducing voltage; and an attenuation
facilitating voltage is provided immediately after a fall of the
pulse voltage, the attenuation facilitating voltage having a same
polarity as that of the upper limit voltage, an absolute value of
the pre-charge voltage being set smaller than the pre-charge
voltage.
Because the attenuation facilitating voltage in this case is a
voltage having the same polarity and a smaller absolute value than
that of the minimum discharge-maintaining voltage, this case, in
comparison with the case where the attenuation facilitating voltage
has the opposite polarity, is less effective for improving the
discharge-end response, but enables the droplets discharge with
minimum no-discharge period, and therefore is effective for
formation of contiguous dots. Further, it becomes possible to adopt
a low-voltage driver because the potential difference between the
upper limit voltage and the lower limit voltage of the pulse
voltage becomes small.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, wherein the fluid discharge hole,
provided in the nozzle, has a diameter ranging from 0.01 .mu.m to
25 .mu.m; the electrostatic suction type fluid discharge device
comprises voltage applying means for applying a DC voltage between
the nozzle and the substrate, the DC voltage being equal to or
greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid; and a pre-charge
voltage is provided immediately before starting application of the
DC voltage, the pre-charge voltage having a same polarity as that
of the DC voltage, an absolute value of the DC voltage being set
smaller than the minimum discharge-inducing voltage.
In the above structure, the fluid discharge hole provided in the
nozzle has a miniaturized diameter ranging from 0.01 .mu.m to 25
.mu.m, and therefore the drive voltage can be reduced. This is
greatly beneficial to miniaturization of the device while ensuring
high density, and therefore the same above-described effects as
that of the electrostatic suction type fluid discharge device
according to the present invention is obtained. For example, it
allows the use of a low-voltage driver that offers advantageous
cost performance.
Further, in the above structure in which the voltage applying means
applies a DC voltage between the nozzle and the substrate, and the
DC voltage is set equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid; a pre-charge voltage is provided
immediately before starting application of the DC voltage, the
pre-charge voltage having a same polarity as that of the DC
voltage, an absolute value of the DC voltage being set smaller than
the minimum discharge-inducing voltage. Therefore, the
discharge-start response at the beginning of voltage application
allows the start-position of discharge to be so controlled
precisely as to be dependent on the end-position of application of
DC voltage.
In other words, the above-described problem regarding the response
at the rise and the fall of the voltage occurs not only in the
pulse voltage but also in the application of the DC voltage, which
is applied when the line-drawing is performed on the substrate.
This has been disabling precise adjustment of the start-position
due to the discharge response at the beginning of discharge after
the application of DC voltage, and therefore the stat-position has
not directly correspond to application of the DC voltage. However,
the above structure achieves precise adjustment of discharge-start
position and makes it directly depend on application of the DC
voltage.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, wherein the fluid discharge hole,
provided in the nozzle, has a diameter ranging from 0.01 .mu.m to
25 .mu.m; the electrostatic suction type fluid discharge device
comprises voltage applying means for applying a DC voltage between
the nozzle and the substrate, the DC voltage being equal to or
greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid; and an
attenuation facilitating voltage is provided immediately after an
end of application of the DC voltage, the attenuation facilitating
voltage having an opposite polarity to that of the DC voltage.
In the above structure, the fluid discharge hole provided in the
nozzle has a miniaturized diameter ranging from 0.01 .mu.m to 25
.mu.m, and therefore the drive voltage can be reduced. This is
greatly beneficial to miniaturization of the device while ensuring
high density, and therefore the same above-described effects as
that of the electrostatic suction type fluid discharge device
according to the present invention is obtained. For example, it
allows the use of a low-voltage driver that offers advantageous
cost performance.
Further, in the above structure in which the voltage applying means
applies a DC voltage between the nozzle and the substrate, and the
DC voltage is set equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid; a pre-charge voltage is provided
immediately before starting application of the DC voltage, the
pre-charge voltage having a same polarity as that of the DC
voltage, an absolute value of the DC voltage being set smaller than
the minimum discharge-inducing voltage. Therefore, the
discharge-start response at the beginning of voltage application
allows the start-position of discharge to be so controlled
precisely as to be dependent on the end-position of application of
DC voltage.
As in the control for the application-start-position, when the
line-drawing is performed on the substrate, the problem of
discharge-end response at the end of the voltage application has
been disabling precise adjustment of the end-position, and
therefore the end-position has not directly correspond to end of
application of the DC voltage. However, the above structure
achieves precise adjustment of discharge-end-position and makes it
directly depend on the end of application of the DC voltage.
Further, it is preferable in the electrostatic suction type fluid
discharge device according to the present invention that an
absolute value of the attenuation facilitating voltage is set
smaller than the minimum discharge-inducing voltage.
This is due to the following reason. If the attenuation
facilitating voltage is greater than the absolute value of the
minimum discharge-inducing voltage, the meniscus surface potential
becomes greater on the opposite polarity side than the minimum
discharge-inducing voltage, although it depends upon the
application time of the attenuation facilitating voltage such as
the period of the pulse voltage. This may induce discharge of
fluid, as the fluid is charged to the opposite polarity. Therefore,
it is preferable that the absolute value be set smaller than that
of the minimum discharge-inducing voltage so as to prevent the
meniscus surface potential from turning into the opposite polarity.
As described above, an electrostatic suction type fluid discharge
method according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle onto a
substrate opposite to the nozzle, wherein the fluid discharge hole,
provided in the nozzle, has a diameter ranging from 1 .mu.m to 5
.mu.m. The method comprises the step of applying a voltage between
the nozzle and the substrate, the voltage being equal to or greater
than a minimum discharge-inducing voltage, that is a voltage
required to start discharge of the fluid, wherein a pre-charge
voltage is provided immediately before a rise of the voltage, the
pre-charge voltage having a same polarity as that of the voltage,
an absolute value of the voltage being set smaller than the minimum
discharge-inducing voltage. As described above, the fluid discharge
hole provided in the nozzle has a micro diameter ranging from 0.01
.mu.m to 25 .mu.m, and therefore the drive voltage can be reduced.
This is greatly beneficial to miniaturization of the device while
ensuring high density. It allows the use of a low-voltage driver
that offers advantageous cost performance, and also realizes a
structure not using a counter electrode
In addition, a pre-charge voltage is applied immediately before the
rise of the voltage, which pre-charge voltage has the opposite
polarity to the applied voltage with a smaller absolute value than
that of the minimum discharge-inducing voltage, and therefore the
meniscus surface potential can be previously charged, obtaining
more desirable discharge-start response.
Further, as described above, another electrostatic suction type
fluid discharge method according to the present invention
discharges by electrostatic suction a fluid, which is electrically
charged by voltage application, from a fluid discharge hole of a
nozzle onto a substrate opposite to the nozzle, wherein the fluid
discharge hole, provided in the nozzle, has a diameter ranging from
0.01 .mu.m to 25 .mu.m. The method comprises the step of applying a
voltage between the nozzle and the substrate, the voltage being
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid, wherein an
attenuation facilitating voltage is provided immediately after a
fall of the voltage, the attenuation facilitating voltage having an
opposite polarity to that of the voltage.
As described above, the fluid discharge hole provided in the nozzle
has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, and
therefore the drive voltage can be reduced. This is greatly
beneficial to miniaturization of the device while ensuring high
density. It allows the use of a low-voltage driver that offers
advantageous cost performance, and also realizes a structure not
using a counter electrode
Further, since an attenuation facilitating voltage having the
opposite polarity to that of the applied voltage is applied
immediately after the fall of the voltage, the attenuation of the
meniscus surface potential is facilitated and the separation of the
fluids is ensured. Therefore, more desirable discharge-end response
is obtained.
[Second Embodiment]
As described above, in an electrostatic suction type fluid
discharge method by the fluid discharge model using a local
electric field, it is possible to simultaneously reduce a diameter
of nozzle and a drive voltage.
However, in the electrostatic suction type fluid discharge method
by the fluid discharge model using a local electric field, the
discharge response is determined basically by an electric
resistance R and a time constant RC. The electric resistance R is
an electric resistance of the fluid between the electrode in the
nozzle and the tip of the nozzle, and the time constant RC is a
product of an electrostatic capacitance C between the substrate and
the meniscus on the tip of nozzle. A parameter of the electric
resistance R and the electrostatic capacitance C includes a nozzle
diameter d. The discharge response is changed according to the
nozzle diameter d. As described above, the time constant RC
extremely increases as the nozzle diameter decreases. This
decreases discharge response, and also decreases the frequency
limit to cause discharge.
More specifically, in an electrostatic suction type fluid discharge
by the fluid discharge model using a local electric field, the
discharge response is basically changed by the electric resistance
of the fluid (discharge material) between the electrode in the
nozzle and the tip of nozzle. Therefore, the discharge response can
be greatly varied depending upon the electric conductivity of the
fluid. Because of this, if the relative speed between the nozzle
and the substrate is not adequate, or if the voltage applied
between the nozzle and the substrate is not adequate, the line
drawing may become unstable.
For example, a fluid with a low conductivity has poor discharge
response, and therefore, as illustrated in FIG. 17, if the relative
movement of the discharge head 110 and the substrate stage 16 on
which the substrate 13 is placed is performed at a high speed, the
resulting picture will be an intermittent line even with
application of bias voltage, in contrast to the low-speed driving
by which the line becomes smooth and continuous.
Such problem results from the micro diameter of the tip of nozzle
in the electrostatic suction type fluid discharge by the fluid
discharge model using a local electric field. The problem is caused
by (i) deterioration in the discharge response due to increase of
the electric resistance of the fluid (discharge material) between
the electrode in the nozzle and the tip of the nozzle, and (ii)
super-miniaturization of the diameter/width of the dot/line that is
formed on the substrate. This is a new problem to be solved that
was not an issue in the conventional discharge amount.
An electrostatic suction type fluid discharge device according to
the present embodiment controls the scanning speed or the applied
voltage between the nozzle and the substrate, so as to ensure
stable drawing of continuous line. The following concretely
describes two exemplary structures of such electrostatic suction
type fluid discharge device. For the purpose of convenience, the
same reference numerals are given to the members having the same
functions as that of the members used in the First Embodiment, and
description thereof is omitted.
(Second Embodiment 1)
FIG. 18 is a view illustrating a cross section of lateral side of
major part of an electrostatic suction type fluid discharge device
according to the present embodiment.
In the electrostatic suction type fluid discharge device, the
substrate stage 16 is disposed to be opposite to the nozzle hole of
the nozzle 1, with a certain interval therebetween. This layout
allows the discharge material discharged from the nozzle hole of
the nozzle 1 to be stably landed on the surface of the substrate
13. The substrate stage 16 also functions as the counter electrode
14. The substrate 13 is placed on the substrate stage 16.
In the present embodiment, the substrate stage 16 is given a
function as the counter substrate. However, as described above, in
the present invention, due to the conversion effect of the electric
field at the tip of the nozzle, and the action of the image force
exerted on the counter substrate, it is not necessary to dispose a
counter electrode at a rear side of the substrate. Moreover, unlike
the conventional structure, the present invention does not require
a conductive substrate. Therefore, an insulating glass substrate, a
plastic substrate such as polyimide, a ceramics substrate, a
semiconductor substrate or other types of substrate can be
used.
In place of the voltage applying section 9 (see FIG. 9), a drive
signal applying section 109 is connected to the electrode 2 and the
substrate stage 16. The drive signal applying section 109, under
the control by the controller 118, controls at least one of the
signal voltage applied to the electrode 2 and that applied to the
substrate stage 16. The drive signal applying section 109 applies a
pulse voltage or a DC bias voltage between the tip of the nozzle 1
and the substrate 13. The drive signal applying section 109 applies
the pulse voltage for one-shot flow discharge, or a DC bias voltage
for a continuous discharge of fluids. A positive or negative
voltage may be arbitrarily used for this voltage applied between
the tip of the nozzle 1 and the substrate 13. Further, the
substrate stage 16 may be grounded.
The electrostatic suction type fluid discharge device according to
the present embodiment further includes a head drive section 116, a
controller 117, and a stage drive section 119. The head drive
section 116 at least drives the discharge head 110 in the
X-direction. The stage drive 119 at least drives the substrate
stage 16 in the opposite direction to the X-direction. It may be
arranged so that only one of the substrate stage 16 and the
discharge head 110 is driven. The head drive section 116 and the
stage drive section 119 are controlled by the controller 117. As
shown in FIG. 19, the scanning speed v designates a relative speed,
that is a sum of (i) a speed v.sub.H of the discharge head 110 in
the X-direction and (ii) a speed v.sub.S of the substrate stage 16
in the opposite direction to the X-direction.
In this structure, the nozzle 1 and the substrate 13 are relatively
moved by the controllers 117 and 118, the stage drive section 119,
the substrate stage 16, the discharge head 110, the head drive
section 116, and the drive signal applying section 109, while a
voltage is applied between the nozzle 1 and the substrate 13. In
this way, these components function as line-drawing means for
drawing a line.
FIG. 20 shows a waveform of a drive signal applied between a nozzle
1 and a substrate 13. The following describes discharge
characteristics of the electrostatic suction type fluid discharge,
with reference to FIG. 20. Basically, when the drive signal
application section 109 applies a drive signal to the electrode 2
in the nozzle 1 of the discharge head 110 and to the substrate
stage 16, a signal voltage 111, which is determined by a potential
difference therebetween, is applied between the nozzle 1 and the
substrate 13.
The signal voltage 111 is equal to or greater than the minimum
discharge-inducing voltage (indicated by dot lines in the figures).
Because the diameter/width of the dot/line formed by fluid landed
on the substrate can be minimized by performing the discharge at
the minimum discharge-inducing voltage 130, the signal voltage 111
is set around the minimum discharge-inducing voltage for each
nozzle. With this arrangement, stable drawing of super-micro dot or
a super-micro line is ensured.
The minimum discharge-inducing voltage 130 designates a minimum
voltage condition to cause discharge in a case where fluid is
discharged by a direct current bias. The minimum discharge-inducing
voltage 130 depends upon the nozzle diameter. When the surface
potential of meniscus formed by fluid of the tip of the nozzle 1
(nozzle hole) reaches the minimum discharge-inducing voltage 130,
discharge starts.
When the signal voltage 111 is applied, electric charge starts
flowing from the electrode 2, and the electric charge starts to be
accumulated on the meniscus formed by the fluid of the tip of the
nozzle 1 (nozzle hole). A meniscus surface potential 120 (indicated
by a broken line in the figures) that is a potential curve of the
meniscus surface draws a saturated curve, and its saturation speed
depends upon (i) an applied signal voltage 111, (ii) an electric
conductivity of fluid that is the discharge material 3, and (iii) a
shape of the fluid path in the nozzle 1.
When the meniscus surface potential 120 reaches the minimum
discharge-inducing voltage 130, a very few amount of fluid is
discharged in response to the generated electric field force. After
the fluid is discharged, the meniscus surface potential 120 once
becomes lower than the minimum discharge-inducing voltage 130, and
therefore, the discharged fluid becomes a thread-like form, before
the thread of fluid is finally cut at the tip of the nozzle 1.
Then, as an electric charge is again supplied to the meniscus
surface potential 120 from the electrode 2, the meniscus surface
potential starts increasing again. When the meniscus surface
potential 120 reaches the minimum discharge-inducing voltage 130
again, the discharge of fluid is re-started. This cycle is
repeatedly carried out. In other words, after the discharge is
started, decrease in potential due to fluid discharge and increase
in potential due to accumulation of electric charge from the
electrode alternately occur. As a result, the meniscus surface
potential 120 exhibits pectination-like transition in the vicinity
of the minimum discharge-maintaining voltage. With such a period,
the discharge is repeated intermittently.
This period of intermittent discharge t.sub.v differs depending
upon the signal voltage 111 and the electric conductivity of the
fluid. For example in a case where the discharge is performed with
the applied voltage of 300V using a discharge material made of
silver nano paste whose electric conductivity is approximately
10.sup.-8 S/cm and a discharge head with the nozzle diameter of
approximately 2 .mu.m, the period of intermittent discharge t.sub.v
is approximately 66 .mu.sec.
With regard to the line-drawing condition, as shown in FIG. 21(a),
the discharge interval on the substrate is determined by a product
vxt.sub.v of the scanning speed v and the period of intermittent
discharge t.sub.v that depends on every discharge condition. If the
discharge interval vxt.sub.v is equal to the pattern width of the
discharge pattern of droplet (dot) P in the scanning direction, the
single discharge patterns are formed on one direct line without
overlaying each other. In order to ensure stable line-drawing, it
is preferable that the single discharge patterns adjacent in the
scanning direction are slightly overlaid. Therefore, as illustrated
in FIG. 21(b), the scanning speed v is determined such that the
adjacent droplet discharge patterns P-P are overlaid by a width
that is equal to or wider than a half of the pattern width D in the
sub-scanning direction. In this way, the patterns P-P are securely
connected and therefore will not be separated, and stable
line-drawing is ensured at all times.
Here, the following explains the reason why the overlaid width is
set equal to or wider than a half of the pattern width D in the
sub-scanning direction. As shown in FIG. 21(c), the single
discharge pattern P depends upon the scanning speed v. The faster
the scanning speed v is, the longer the signal discharge pattern P
in the scanning direction is. However, the pattern width D in the
sub-scanning direction does not depend upon the scanning speed v
and therefore does not change as greatly as the pattern in the
scanning direction, although it may change slightly.
Further, the scanning speed v becomes slow when the adjacent single
discharge patterns P-P are unnecessarily overlaid. Therefore, the
scanning speed v is controlled such that the adjacent single
discharge patterns P-P are overlaid by the width at or less than
1.5 times the pattern width D in the sub-scanning direction. This
prevents the unnecessary overlay and therefore the excessive
decrease in scanning speed does not occur.
Assumed that the pattern width in the scanning direction is L and
the pattern width in the sub-scanning direction, that is orthogonal
to the scanning direction, is D, the following formula gives
condition to ensure continuous and stable line-drawing at a high
speed while maintaining a super-micro line width.
V<(L-1.5D)/t.sub.v (19)
In the electrostatic suction type fluid discharge device according
to the present embodiment, under the control by the controller 117,
the head drive section 116 and the stage drive section 119 set the
scanning speed v, which is the speed for driving the discharge head
110 and the substrate stage 16, so that the intermittently
discharged adjacent discharge patterns P are partially overlaid. To
ensure this operation, the scanning speed v is determined based
upon the period of intermittent discharge t.sub.v which corresponds
to the electric conductivity of the fluid and the signal voltage
111, and also in accordance with the period of the intermittent
discharge. Specifically, the scanning speed v is set according to
the above Formula (19).
Accordingly, within the range of condition of the set signal
voltage 111, continuous and stable line-drawing can be performed at
a high speed, thereby realizing high speed line drawing.
(Second Embodiment 2)
The following describes an electrostatic suction type fluid
discharge device according to the present embodiment. However, the
electrostatic suction type fluid discharge device according to the
present invention basically has the same structure as that of the
electrostatic suction type fluid discharge device according to the
Second Embodiment (1) described above. Therefore, FIG. 18 is used
again as a diagram illustrating the structure of the device.
Further, only different part will be described below, and the same
part as the Second Embodiment (1) is omitted.
In the electrostatic suction type fluid discharge device according
to the Second Embodiment (1), the signal voltage 111 is set in the
vicinity of the minimum discharge-inducing voltage 130 while
satisfying the condition where the signal voltage 111 is equal to
or greater than the minimum discharge-inducing voltage 130. With
this arrangement, the Second Embodiment (1) achieves stable
line-drawing by changing the scanning speed v. On the other hand,
the electrostatic suction type fluid discharge device according to
the Second Embodiment (2) achieves stable line-drawing by varying
the signal voltage 111.
FIGS. 22(a) and 22(b) show a relationship between a waveform of
signal voltage and a period of intermittent discharge. The
following describes discharge characteristics of the electrostatic
suction type fluid discharge, with reference to these figures. As
described in the Second Embodiment (1), discharge starts when the
meniscus surface potential 120, that starts increasing after the
signal voltage 111 is applied, reaches the minimum
discharge-inducing voltage 130. Once fluid is discharged, a state
of intermittent discharge is maintained by repeating a decrease due
to electric discharge caused by the discharge of fluid and an
increase due to electric charges supplied from the electrode 2.
The speed of increase in meniscus surface potential after the
discharge greatly differs depending upon the signal voltage 111.
For example, as illustrated in FIG. 22(a), in a case where the
applied signal voltage 111 is a low voltage that is substantially
equal to the minimum discharge-inducing voltage 130, the meniscus
surface potential repeats increasing and decreasing in a nearly
saturated state. Therefore, the increasing speed of the meniscus
surface potential 120 is extremely slow. Consequently, the
discharge that starts when the meniscus surface potential 120
reaches the minimum discharge-inducing voltage 130 is performed at
long intervals.
On the other hand, as illustrated in FIG. 22(b), in a case where
the signal voltage 111 is sufficiently greater than the minimum
discharge-inducing voltage 130, the meniscus surface potential 120
repeats increasing and decreasing in distantly saturated state.
Consequently, the discharge that starts when the meniscus surface
potential 120 reaches the minimum discharge-inducing voltage 130 is
performed at short intervals.
Accordingly, even if the same discharge material 3 and the
discharge head 110 having the same nozzle diameter are used, the
intermittent discharge frequency can be changed by changing the
signal voltage 111.
FIG. 23 shows a relationship between the signal voltage 111 and the
intermittent discharge frequency in a case where the discharge is
performed using (i) a silver nano paste manufactured by the HARIMA
CHEMICALS, INC as the discharge material 3, and (ii) the discharge
head 110 having the nozzle diameter of approximately 1 .mu.m. FIG.
23 shows that the greater the signal voltage 111 is, the greater
the intermittent discharge frequency is. Moreover, the greater the
signal voltage 111 is, the shorter the time interval of discharge.
This indicates that a greater signal voltage 111 is more effective
to the line-drawing.
With the silver nano paste and the discharge head 110 with the
nozzle diameter of approximately 1 .mu.m, the relationship between
the scanning speed v and the minimum voltage for causing
line-drawing was examined. As shown in FIG. 24, it was showed that
each of the scanning speed requires different minimum voltage for
line-drawing, and it was also confirmed that the faster the
scanning speed is, the greater the voltage is.
Thus, in the electrostatic suction type fluid discharge device
according to the present embodiment, the drive signal applying
section 109 sets, under the control by the controller 118, the
signal voltage 111 in such a way that the signal voltage 111 is set
equal to or greater than the minimum voltage for line-drawing, at
which voltage the interval between single discharge pattern of the
intermittent discharge becomes zero, according to the specified
scanning speed v.
Specifically, as with the Second Embodiment (1), as shown in FIG.
21(b), the signal voltage 111 is set such that the width of
overlaying single discharge patterns P-P, that are adjacent to each
other in the scanning direction, is set within a range of not less
than 0.5 times but not more than 1.5 times the pattern width D in
the sub-scanning direction.
In this way, continuous and stable line-drawing is securely
performed within the specified condition of scanning speed v, and
therefore a high speed line-drawing can be performed.
Further, according to FIG. 24, the following formula for
determining the scanning speed v (mm/sec) and the minimum signal
voltage for causing line-drawing V.sub.in (V) is given to easily
realize high speed line-drawing when using the discharge material 3
having the electric conductivity of 10.sup.-7-10.sup.-9 S/cm, such
as the silver nano paste. .fwdarw.V.sub.in>31.sub.v+75 (20)
For example, in order to perform stable line-drawing during a high
speed scanning at a speed equal to or faster than 5 mm/sec, it is
necessary to apply a voltage of 300V or greater.
In view of the object of ensuring stable line-drawing, the present
embodiment describes separate structures for optimizing the
scanning speed v and the signal voltage 111, respectively. However,
the line width of the line-drawing tends to be wider and wider as
the signal voltage 111 is continuously increased from the minimum
discharge-inducing voltage 130. In this view, a necessary line
width and a necessary scanning speed v can be obtained by
optimizing the scanning speed v and the signal voltage 111 at the
same time.
As described above, an electrostatic suction type fluid discharge
device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle of a
discharge head onto a substrate opposite to the nozzle, wherein the
fluid discharge hole, provided in the nozzle, has a diameter
ranging from 0.01 .mu.m to 25 .mu.m; and the electrostatic suction
type fluid discharge device comprises line-drawing means for
applying a voltage between the nozzle and the substrate while
relatively moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid, the line-drawing means controlling a speed
of the relative movement so that adjacent ones of discharge pattern
are partly overlaid with each other, in accordance with a period of
intermittent discharge which is performed at a frequency depending
on the voltage and an electric conductivity of the fluid.
With the above structure in which the fluid discharge hole provided
in the nozzle has a diameter ranging from 0.01 .mu.m to 25 .mu.m, a
local electric field is generated in accordance with the discharge
model using a local electric field. On this account,
miniaturization of nozzle achieves a decrease in drive voltage for
discharging. Such reduction of the drive voltage is greatly
beneficial to miniaturization of the device and an increase in
density. It may be obvious but, this reduction of the drive voltage
allows the use of a low-voltage driver that offers advantageous
cost performance.
Moreover, in the discharge model using the local electric field,
the electric field strength required for discharge depends upon the
converged local electric field strength, and therefore the counter
electrode can be omitted. In other words, it becomes possible to
carry out printing on an insulating substrate without using a
counter electrode, allowing more flexible device arrangement.
Further, it also becomes possible to print on a thick
insulator.
However, in the above structure, the discharge response basically
depends upon the electric resistance of fluid (discharge material)
between the electrode in the nozzle and the tip of nozzle, and
therefore, the discharge response may be extremely changed by a
change in electric conductivity of the fluid. In this case, stable
line-drawing may not be performed depending upon the relative speed
between the nozzle and the substrate or the voltage applied between
the nozzle and the substrate. This problem occurs as a consequence
of miniaturization of the diameter of the tip of the nozzle, which
makes the diameter/width of the dot/line formed on the substrate to
be super miniaturized. In addition to this, an increase in electric
resistance as a result of miniaturization of nozzle which results
in deterioration in discharge response also contributes to the
problem. This is a new problem that would not have been an issue in
the conventional discharge amount.
On the other hand, in the above structure, the line-drawing means
applies a voltage between the nozzle and the substrate while
relatively moving the nozzle and the substrate so as to carry out
line-drawing, which voltage is equal to or greater than the minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid. Further, the line-drawing means controls a
speed of the relative movement so that adjacent ones of discharge
pattern are partly overlaid with each other, in accordance with a
period of intermittent discharge which is performed at a frequency
depending on the voltage and an electric conductivity of the fluid.
Therefore, a continuous and stable line-drawing can be performed at
a high speed without causing errors such as an inappropriately
widened line width, while setting the voltage in the vicinity of
the minimum discharge-inducing voltage that is a voltage required
for drawing super micro line.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which electrostatic suction type
fluid discharge device is electrically charged by voltage
application, from a fluid discharge hole of a nozzle of a discharge
head onto a substrate opposite to the nozzle, wherein the fluid
discharge hole, provided in the nozzle, has a diameter ranging from
0.01 .mu.m to 25 .mu.m; and the electrostatic suction type fluid
discharge device comprises line-drawing means for applying a
voltage between the nozzle and the substrate while relatively
moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid, the line-drawing means controlling the
voltage so that adjacent ones of discharge pattern are partly
overlaid with each other, the discharge pattern being discharged
intermittently, and being determined depending on a speed of the
relative movement.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, so
that the drive voltage can be reduced. This is greatly beneficial
to miniaturization of the device while ensuring high density, and
therefore the same above-described effects as that of the
electrostatic suction type fluid discharge device according to the
present invention is obtained. For example, it allows the use of a
low-voltage driver that offers advantageous cost performance.
Further, in the above structure, the line-drawing means applies a
voltage between the nozzle and the substrate while relatively
moving the nozzle and the substrate so as to carry out
line-drawing, which voltage is equal to or greater than minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid. Here, the voltage applied between the
nozzle and the substrate is so controlled that adjacent ones of
discharge pattern are partly overlaid with each other, which
discharge pattern are discharged intermittently and determined
depending on a speed of the relative movement. Therefore, the
frequency of intermittent discharge can be increased to accommodate
high speed movement, and a continuous and stable line-drawing can
be performed at a desired high speed.
It is preferable in the electrostatic suction type fluid discharge
device described above that the line-drawing means control the
voltage or the speed of the relative movement so that the adjacent
ones of discharge pattern are overlaid with each other by 0.5 to
1.5 times of a vertical diameter of each pattern, the vertical
diameter being a diameter orthogonal to a direction of the relative
movement.
A pattern diameter of the discharge pattern in the relative
movement direction is changed according to the relative movement
speed. However, the pattern diameter in a vertical direction to the
relative movement direction is less affected by the relative
movement speed. In view of this, the voltage or the speed of the
relative movement is controlled so that the adjacent ones of
discharge pattern are overlaid with each other by 0.5 to 1.5 times
a vertical diameter of each pattern, which vertical diameter is a
diameter orthogonal to a direction of the relative movement. This
assures stable performance of the line-drawing. Besides, the
patterns will not be overlaid too much, and therefore the desired
drive speed can be ensured. As well as this, excessive increase in
voltage is also avoided.
As described above, another electrostatic suction type fluid
discharge device according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle of a
discharge head onto a substrate opposite to the nozzle, wherein the
fluid discharge hole, provided in the nozzle, has a diameter
ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic suction type
fluid discharge device comprises line-drawing means for applying a
voltage between the nozzle and the substrate while relatively
moving the nozzle and the substrate so as to carry out
line-drawing, the voltage being equal to or greater than a minimum
discharge-inducing voltage, that is a voltage required to start
discharge of the fluid, the line-drawing means carrying out line
drawing with a scanning speed and a voltage specified as:
V.sub.in>31 v+75, where v (mm/sec) denotes the scanning speed,
and V.sub.in denotes the voltage, provided that an electric
conductivity of the fluid is in a range of 10.sup.-7-10.sup.-9
S/cm.
In the above structure, the fluid discharge hole provided in the
nozzle has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, so
that the drive voltage can be reduced. This is greatly beneficial
to miniaturization of the device while ensuring high density, and
therefore the same above-described effects as that of the
electrostatic suction type fluid discharge device according to the
present invention is obtained. For example, it allows the use of a
low-voltage driver that offers advantageous cost performance.
In the above structure, when applying a voltage between the nozzle
and the substrate while relatively moving the nozzle and the
substrate so as to carry out line-drawing, which voltage is equal
to or greater than a minimum discharge-inducing voltage, that is a
voltage required to start discharge of the fluid, the line-drawing
means carries out line drawing with a scanning speed and a voltage
specified as: V.sub.in>31 v+75, where v (mm/sec) denotes the
scanning speed, and V.sub.in denotes the voltage, provided that an
electric conductivity of the fluid is in a range of
10.sup.-7-10.sup.-9S/cm. Therefore, the discharged material is
limited to material with an electric conductivity of
10.sup.-7-10.sup.-9 S/cm, such as silver nano paste. However,
stable and easy line-drawing can be performed at a high speed.
As described above, in an electrostatic suction type fluid
discharge method according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle of a
discharge head onto a substrate opposite to the nozzle, wherein,
the fluid discharge hole provided in the nozzle has a diameter
ranging from 0.01 .mu.m to 25 .mu.m, the electrostatic suction type
fluid discharge method includes the step of applying a voltage
between the nozzle and the substrate while relatively moving the
nozzle and the substrate so as to carry out line-drawing, the
voltage being equal to or greater than a minimum discharge-inducing
voltage, that is a voltage required to start discharge of the
fluid. The electrostatic suction type fluid discharge device
controls a speed of the relative movement so that adjacent ones of
discharge pattern are partly overlaid with each other, in
accordance with a period of intermittent discharge which is
performed at a frequency depending on the voltage and an electric
conductivity of the fluid.
As described above, the fluid discharge hole provided in the nozzle
has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, and
therefore the drive voltage can be reduced. This is greatly
beneficial to miniaturization of the device while ensuring high
density. It allows the use of a low-voltage driver that offers
advantageous cost performance, and also realizes a structure not
using a counter electrode.
In addition, the speed for relative movement is set so that
adjacent ones of discharge pattern are partly overlaid with each
other, in accordance with a period of intermittent discharge which
is performed at a frequency depending on the voltage and an
electric conductivity of the fluid. This allows stable and
high-speed line-drawing while maintaining super micro line
width.
As described above, another electrostatic suction type fluid
discharge method according to the present invention discharges by
electrostatic suction a fluid, which is electrically charged by
voltage application, from a fluid discharge hole of a nozzle of a
discharge head onto a substrate opposite to the nozzle, wherein the
fluid discharge hole provided in the nozzle has a diameter ranging
from 0.01 .mu.m to 25 .mu.m, the electrostatic suction type fluid
discharge method comprising the step of applying a voltage between
the nozzle and the substrate while relatively moving the nozzle and
the substrate so as to carry out line-drawing, the voltage being
equal to or greater than a minimum discharge-inducing voltage, that
is a voltage required to start discharge of the fluid. The
electrostatic suction type fluid discharge device controls the
voltage so that adjacent ones of discharge pattern are partly
overlaid with each other, the discharge pattern being discharged
intermittently, and being determined depending on a speed of the
relative movement.
As described above, the fluid discharge hole provided in the nozzle
has a micro diameter ranging from 0.01 .mu.m to 25 .mu.m, and
therefore the drive voltage can be reduced. This is greatly
beneficial to miniaturization of the device while ensuring high
density. It allows the use of a low-voltage driver that offers
advantageous cost performance, and also realizes a structure not
using a counter electrode.
Further, the voltage applied between the nozzle and the substrate
is so controlled that adjacent ones of discharge pattern are partly
overlaid with each other, which discharge pattern are discharged
intermittently and determined depending on a speed of the relative
movement. Therefore, the speed and the voltage are optimized, and a
continuous and stable line-drawing can be performed at a desired
high speed.
[Third Embodiment]
The present invention explains a result of test for examining
required condition of drive voltage in discharging a micro droplet
of liquid from a super micro nozzle from a super micro nozzle by
electrostatic force. In the embodiment below, a counter electrode
is disposed to generate an electric field between the nozzle and
the counter electrode (i.e. discharge target grounded via the
counter electrode), so as to ensure stable discharge of liquid
(fluid) with respect to the discharge target.
This electrostatic suction type fluid discharge device employs a
discharge method using an electrostatic suction effect, which is
carried out with a fluid discharge model using a local electric
field. As described above, this electrostatic suction type fluid
discharge device achieves both miniaturization of nozzle diameter
and reduction in drive voltage by using a nozzle whose diameter
ranges from 0.01-25 .mu.m.
However, when forming a particularly tiny dot or a particularly
thin line by this electrostatic suction type fluid discharge
device, the potential difference between the drive voltage for
driving inside the nozzle and that of the substrate (the target
provided in front of the counter substrate) becomes an important
factor. More specifically, an excessively large potential
difference results in an excessive amount of discharge fluid, but
an excessively small potential difference results in discharge
failure.
Further, another important factor is application time with respect
to the voltage value. That is, if an excessively long application
time is set to a certain voltage value, it results in an excessive
amount of discharge fluid and therefore a micro pattern cannot be
formed, but an excessively short application time results in
discharge failure.
In view of this, the present embodiment ensures appropriate
settings for the voltage (drive voltage) applied between the nozzle
and the counter electrode, and for the application time thereof, so
as to ensure stable formation of micro dot pattern. Note that, for
ease of explanation, materials having the equivalent functions as
those shown in the drawings pertaining to the foregoing First and
Second Embodiments will be given the same reference symbols, and
explanation thereof will be omitted here.
(Third Embodiment 1)
FIGS. 25(a), 25(b), FIG. 26, FIG. 27(a) through 27(c) show the
fluid discharge method performed by the electrostatic suction type
fluid discharge device according to the present embodiment. FIG.
25(a) illustrates a schematic diagram of an electrostatic suction
type fluid discharge device, and FIG. 25(b) illustrates an
equivalent circuit in the device. FIG. 26 is a graph showing a
relationship between application time and magnitude of
discharge-start voltage (minimum discharge-inducing voltage), for
the voltage applied between the nozzle 1 and the counter electrode
14 (substrate 13). FIGS. 27 (a) through 27(c) are graphs each
showing a relationship between an increase in meniscus surface
potential and condition for starting discharge.
As shown in FIG. 25(a), the electrostatic suction type fluid
discharge device includes the nozzle 1 and the counter electrode 14
which are opposed to each other. The counter electrode 14 is
grounded. The electrode (drive electrode) 2 is provided inside the
nozzle 1, and a power source (drive voltage applying means) 214 is
connected to the electrode 2. The nozzle 1 is filled with the
discharge material (fluid) 3, which is constituted of a fluid. The
substrate (discharge target member) 13, as the discharge target, is
so provided on one side of the counter electrode 14 as to be
opposed to the nozzle 1. The substrate 13 is grounded via the
counter electrode 14. The discharge material is discharged from the
nozzle 1 so as to form, for example, a micro wire pattern, on the
substrate 13.
The power source 214 is controlled by the control device (drive
voltage applying means) 217 constituted of a computer or the like.
More specifically, a discharge signal is supplied to the power
source 214 from the control device 217, and a voltage having wave
form is applied from the power source 214 according to the
discharge signal so as to charge the discharge material 3 inside
the nozzle 1. FIG. 28 shows an example of the drive voltage.
The substrate 13 is made of an insulative glass substrate, a
plastic (polyimide etc.) substrate, a ceramic substrate or a
semiconductor substrate.
The following explains a basic characteristic of micro droplet
discharge method performed by the electrostatic suction type fluid
discharge device, particularly regarding a surface potential
results from electric charge accumulated in the meniscus 240 on the
tip of nozzle 1.
In the electrostatic suction type fluid discharge device shown in
FIG. 25(a), a drive voltage is applied from the power source 214 to
the electrode 2 so that an electric charge is supplied from the
electrode 2 to the discharge material 3. The electric charge is
assumed to move to the meniscus 240 having electrostatic
capacitance formed on the tip of nozzle 1 so that it faces to the
substrate 13. Therefore, as shown in FIG. 25(b), the structure in
FIG. 25(a) can be expressed as a series circuit constituted of
V.sub.0 as a drive voltage applied from the power source 214 to the
electrode 2, R as an electric resistance of the discharge fluid 3
inside the nozzle 1, and C as an electrostatic capacitance between
the meniscus 240 and the substrate 13.
For the series circuit constituted of V.sub.0, R and C, the
relationship between V.sub.0, R and C may be denoted by the
accumulated charge Q(t) on the meniscus 240.
RdQ(t)/dt+Q(t)/C=V.sub.0 (21)
According to the foregoing differential equation, the accumulated
charge Q (t) on the meniscus surface and the surface potential V(t)
are denoted by the following Formulas (22) and (23).
Q(t)=CV.sub.0[1-exp(-t/RC)] (22) V(t)=V.sub.0[1-exp(-t/RC)]
(23)
The following explains an examination result shown in FIG. 26. This
is a result of test using the silver nano paste as the discharge
material 3. This figure shows a relationship between the
discharge-start voltage and application time. The discharge-start
voltage (minimum discharge-causing voltage) designates a minimum
value of voltage applied to the electrode 2 to cause the discharge
material 3 to be discharged from the nozzle 1.
As shown in FIG. 26, the shorter the application time is, the
greater the voltage required for discharge is. This shows that the
condition for starting discharge is related to both the magnitude
of applied voltage (drive voltage) and the application time.
FIGS. 27(a) through 27(c) show a change in surface potential of
meniscus 240 until it reaches the discharge-start voltage. The
figures show respective cases for three different values of voltage
applied from the power source 214 to the electrode 2. These values
of FIGS. 27(a) through 27(c) are obtained from calculation
according to Formula (23) using the values shown in FIG. 26. The
respective values of applied voltage and application time in 27(a)
through 27(c) are taken from three different points in the graph of
FIG. 26. The voltages and times are 440V and 2400 .mu.sec for FIG.
27(a), 680V and 1200 .mu.sec for FIG. 27(b), and 1600V and 400
.mu.sec for FIG. 27(c).
In each case of FIGS. 27(a) through 27(c), application of voltage
from the power source 214 to the electrode 2 causes electric charge
to flow into the discharge material 3, and the charge is started to
be accumulated in the surface of meniscus 240. At this point, as
shown in FIGS. 27(a) through 27(c), the meniscus surface potential
increases as a saturation curve at the speed depending on the
voltage V.sub.0 and the time constant RC in Formula (23).
The meniscus surface potential increasing according to the applied
voltage reaches the discharge-start voltage, that is the minimum
required condition for discharge, when the predetermined time
elapsed. That is, when the voltage is applied for a certain time
for which the meniscus surface potential reaches the
discharge-start voltage, the discharge material 3 is started to be
discharged. To be more specific, by setting the drive voltage
V.sub.0 and the application time t so that the meniscus surface
potential V(t) becomes greater than the discharge-start voltage
VDC, the discharge is ensured. This condition is denoted by the
Formula (24) as follows. VDC.ltoreq.V.sub.0[1-exp(-t/RC)] (24)
Note that, the discharge-start voltage VDC here denotes a minimum
value for applied voltage on condition that the application is
carried out for a sufficient duration. The value here is for DC
bias.
As described, the electrostatic suction type fluid discharge device
is capable of securely setting the potential in the surface of
meniscus produced in the tip of nozzle 1 to be not less than the
discharge-start potential of discharge material 3. Therefore,
stable micro dot formation is performed.
Further, FIG. 29 is a graph showing a relationship between nozzle
diameter (diameter of nozzle hole of nozzle 1) and discharge-start
voltage of the discharge material 3 to be discharged from the
nozzle 1 in the electrostatic suction type fluid discharge device
according to the present embodiment. In this figure, the
relationship between the discharge-start voltage and nozzle
diameter is examined when applying a DC bias to silver nano paste
as the discharge material 3.
As shown in FIG. 29, the discharge-start voltage decreases as the
nozzle diameter decreases, and the discharge-start voltage becomes
approximately 140V when the nozzle diameter becomes 1 .mu.m. That
is, when the nozzle 1 is realized by a nozzle with a
diameter=.phi.1 .mu.m or greater, a DC bias of 130V or greater is
required to be applied so as to ensure stable discharge.
More specifically, according to the fact that the discharge-start
voltage VDC is 130V, as found by the Formula (24):
VDC.ltoreq.V.sub.0 [1-exp(-t/RC)], for the nozzle with a
diameter=.phi.1 .mu.m to .phi.5 .mu.m, the drive voltage V.sub.0
and the application time t need to be determined according to the
following Formula (25) with respect to all voltage waveforms. With
this condition, stable discharge of micro liquid is ensured.
130V<V.sub.0[1-exp(-t/RC)] (25)
As described, for the nozzle 1 with a diameter=.phi.1 .mu.m to
.phi.5 .mu.m, the drive voltage V.sub.0 and the application time t
are determined according to the foregoing Formula (25). With this
arrangement, the electrostatic suction type fluid discharge device
of the present embodiment ensures stable discharge of micro
liquid.
Note that, the foregoing range of nozzle diameter from .phi.1 .mu.m
to .phi.5 .mu.m derives from the fact that the technical lower
limit in formation of nozzle diameter is .phi.1 .mu.m. Further, the
upper limit of .phi.5 .mu.m is a nozzle diameter enabling drawing
of 10 .mu.m line, which is a micro line on general demand, when the
line is drawn on the substrate 13 by the electrostatic suction type
fluid discharge device.
Further, since the voltage required to drive the nozzle 1 is a
potential difference between the signal applied to the electrode 2
inside the nozzle 1 and the signal applied to the counter electrode
14, the form of signals applied to the respective electrodes may
have arbitrary forms. Further, a plus voltage or a minus voltage
may be arbitrary used as the drive voltage.
(Third Embodiment 2)
The following describes another embodiment of the present
embodiment with reference to figures. FIG. 30 is a graph showing a
relationship between (i) a discharge-start voltage (minimum
discharge-inducing voltage) and (ii) a distance between the tip of
nozzle and a substrate (distance between the tip of nozzle 1 and
the substrate 13) for an electrostatic suction type fluid discharge
device according to the present embodiment which has the structure
shown in FIG. 25. The electrostatic suction type fluid discharge
device has a nozzle with a diameter=.phi.1 .mu.m to .phi.5 .mu.m.
The present embodiment describes only different part from Third
Embodiment 1 will be described below, and the same part is
omitted.
FIG. 30 is a graph showing a relationship between (i) a
discharge-start voltage and (ii) a distance between the tip of
nozzle and a substrate, for each case of nozzle diameters of
.phi.1.2 .mu.m, .phi.1.8 .mu.m, .phi.2.4 .mu.m and .phi.4.2 .mu.m,
when the discharge material is realized by silver nano paste.
As shown in FIG. 30, the discharge-start voltage depends on the
distance between the nozzle and the substrate, and therefore
increases as the distance increases. However, when the nozzle
diameter is set within a range of .phi.1 .mu.m to .phi.5 .mu.m, and
the drawing is performed by a nozzle and a substrate having 200
.mu.m or shorter distance therebetween, the voltage applied to the
electrode 2 is set in a range of 130V to 250V, a low and narrow
range.
To be more specific, according to the foregoing Formula (24):
VDC.ltoreq.V.sub.0[1-exp(-t/RC)], the range of discharge-start
voltage is not less than 130v and not more than 250V for a nozzle
with a diameter=.phi.1 .mu.m to .phi.5 .mu.m. Therefore, the drive
voltage V.sub.0 and the application time t need to be determined
according to the following Formula (26) with respect to all voltage
waveforms. With this condition, stable discharge of micro droplet
is ensured. 130V<V.sub.0[1-exp(-t/RC)]<250V (26) As
described, for the nozzle 1 with a diameter=.phi.1 .mu.m to .phi.5
.mu.m, the drive voltage V.sub.0 and the application time t are
determined according to the foregoing Formula (25) in the
electrostatic suction type fluid discharge device of the present
embodiment. With this arrangement, the excessive amount of
discharge or discharge failure is prevented, and stable discharge
of micro droplet is ensured.
Note that, since the voltage required to drive the nozzle 1 is a
potential difference between the signal applied to the electrode 2
inside the nozzle 1 and the signal applied to the counter electrode
14, the form of signals applied to the respective electrodes may
have arbitrary forms. Further, a plus voltage or a minus voltage
may be arbitrary used as the drive voltage.
Here, according to the graph of FIG. 30, the transitions of the
maximum value (VH) and the minimum value (VL) of discharge-start
voltage (minimum discharge-causing voltage) for the nozzle 1 with a
diameter=.phi.1 .mu.m to .phi.5 .mu.m are respectively denoted by
the following general Formulas (27) and (28) where X is a variable
denoting the distance between nozzle and diameter.
VH=-0.001X.sup.2+0.44X+125 (27) VL=-0.0013X.sup.2+0.69X+160
(28)
With the values of VH and VL, the foregoing Formula (26) may be
expressed as follows. VL<V.sub.0[1-exp(-t/RC)]<VH (26)
(Third Embodiment 3)
The following describes still another embodiment of the present
embodiment with reference to figures. FIG. 31 is a graph showing a
relationship between (i) an application voltage (drive voltage) to
the electrode 2 and (ii) variation in meniscus surface potential,
in the electrostatic suction type fluid discharge device according
to the present invention, which has the structure shown in FIG. 25.
The electrostatic suction type fluid discharge device has a nozzle
with a diameter=.phi.1 .mu.m to .phi.5 .mu.m. The present
embodiment describes only different part from Third Embodiment 1 or
2 will be described below, and the same part is omitted. For an
electrostatic suction type fluid discharge device which forms a
micro pattern on the substrate 13, it is important to set the
position of discharge material 3 with high accuracy, and to adjust
the distance between the nozzle and substrate (gap between the
nozzle tip and the substrate) with high accuracy. These factors are
particularly important when forming a micro pattern on the
substrate 13 made with irregular patterns.
Further, the present embodiment examines variation in meniscus
surface potential with respect to a change in distance between the
nozzle and the substrate when applying a pulse drive voltage to the
electrode 2 of the nozzle 1. The result is shown in FIG. 31. In
this case, the discharge material 3 is realized by silver nano
paste, and the nozzle diameter is set in a range of .phi.1 .mu.m to
.phi.5 .mu.m. In FIG. 31, the distance between the nozzle and
substrate is set to 30 .mu.m, and is increased by 10% to examine
variation degree of meniscus surface potential.
As shown in FIG. 31, the variation in meniscus surface potential
greatly varies depending on the value of application voltage to the
electrode 2. As the application voltage increases, the degree of
variation drastically increases. More specifically, when the
variation curve of meniscus surface potential is moved up to a
greater value, a large amount of the discharge material 3 is
suddenly discharged from the nozzle 1. On the other hand, when the
variation curve of meniscus surface potential is moved down to a
smaller value, discharge of the discharge material 3 from the
nozzle 1 suddenly stops.
More specifically, when a high voltage is applied to the electrode
2, sudden increase in discharge amount or sudden stoppage of
discharge is more likely to happen. Therefore, according to FIG.
31, the variation degree of meniscus surface potential is
preferably suppressed to 1V or lower to ensure stable discharge.
This is attained by setting the application voltage to the
electrode 2 to be equal to or lower than 250V.
As described, in the present electrostatic suction type fluid
discharge device using a the nozzle 1 with a diameter falling
within a range between .phi.1 .mu.m and .phi.5 .mu.m, the voltage
value is set to V.sub.0, and the application time is set to t,
which are specified as 130V<V.sub.0[1-exp (-t/RC)<250V, and
the application voltage V.sub.0 is set to 250V or less. With this
arrangement, variation in meniscus surface potential due to
variation in nozzle-substrate distance can be suppressed, allowing
stable discharge of a micro liquid which is required to form a
micro pattern on the substrate 13.
Note that, because the voltage required to drive the nozzle 1 is a
potential difference between the signal supplied to the electrode 2
inside the nozzle 1 and the signal supplied to the counter
electrode 14, the signals supplied to the electrodes may have any
arbitrary forms. Further, a positive or negative voltage may
arbitrarily be used as a drive voltage.
As described, an electrostatic suction type fluid discharge device
according to the present invention applies a drive voltage between
a nozzle and a discharge target by drive voltage supply means so as
to apply an electric charge to a fluid supplied into the nozzle,
and thereby discharges the fluid from a hole of the nozzle to the
discharge target, the hole of the nozzle falling within a range
between .phi.1 .mu.m and .phi.5 .mu.m in diameter, the
electrostatic suction type fluid discharge device outputting the
drive voltage under a condition: a voltage value=V.sub.0, and an
application time=t, which are specified as
VDC<V.sub.0[1-exp(-t/RC)] where R expresses electric resistance
of the fluid, C expresses electric capacitance between the fluid in
a tip of the nozzle and the discharge target, and VDC expresses a
minimum voltage at which the fluid is caused to be discharged in
response to application of the drive voltage.
As described, an electrostatic suction type fluid discharge device
according to the present invention applies a drive voltage between
a nozzle and a discharge target so as to apply an electric charge
to a fluid supplied into the nozzle, and thereby discharges the
fluid from a hole of the nozzle to the discharge target, wherein:
the hole of the nozzle falls within a range between .phi.1 .mu.m
and .phi.5 .mu.m in diameter, the method outputting the drive
voltage under a condition: a voltage value=V.sub.0, and an
application time=t, which are specified as:
130V<V.sub.0[1-exp(-t/RC)] where R expresses electric resistance
of the fluid, and C expresses electric capacitance between the
fluid in a tip of the nozzle and the discharge target.
Further, an electrostatic suction type fluid discharge method
according to the present invention applies a drive voltage between
a nozzle and a discharge target so as to apply an electric charge
to a fluid supplied into the nozzle, and thereby discharges the
fluid from a hole of the nozzle to the discharge target, wherein:
the hole of the nozzle falls within a range between .phi.1 .mu.m
and .phi.5 .mu.m in diameter, the method outputting the drive
voltage under a condition: a voltage value=V.sub.0, and an
application time=t, which are specified as:
130V<V.sub.0[1-exp(-t/RC)] where R expresses electric resistance
of the fluid, and C expresses electric capacitance between the
fluid in a tip of the nozzle and the discharge target.
In the conventional fluid discharge devices, the miniaturization of
the nozzle requires more intense electric field to cause the fluid
to be discharged, and therefore the miniaturization of nozzle
contradicts with decrease in drive voltage. In contrast, the
present invention has achieved both the miniaturization of nozzle
and the decrease in drive voltage with the use of nozzle whose
diameter is specified within the foregoing range. This structure
was made based on such a new finding that a micro nozzle of
.phi.0.01 .mu.m to .phi.25 .mu.m in diameter causes a local
electric field, which allows the fluid to be discharged by a lower
drive voltage.
Further, the present invention has a structure with a specified
nozzle diameter, ranging from .phi.1 .mu.m and .phi.5 .mu.m. With
this structure, the present invention ensures the effect of
decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage for driving nozzle is outputted under a
condition: a voltage value=V.sub.0, and an application time=t,
which are specified as: 130V<V.sub.0[1-exp(-t/RC)], the meniscus
surface potential of the tip of nozzle is securely set to the value
to induce discharge or greater. This increases reliability in
drawing micro dot patterns.
Another electrostatic suction type fluid discharge device according
to the present invention applies a drive voltage between a nozzle
and a discharge target by drive voltage supply means so as to apply
an electric charge to a fluid supplied into the nozzle, and thereby
discharges the fluid from a hole of the nozzle to the discharge
target, the hole of the nozzle falling within a range between
.phi.1 .mu.m and .phi.5 .mu.m in diameter, the electrostatic
suction type fluid discharge device outputting the drive voltage
under a condition: a voltage value=V.sub.0, and an application
time=t, which are specified as:
130V<V.sub.0[1-exp(-t/RC)]<250V where R expresses electric
resistance of the fluid, and C expresses electric capacitance
between the fluid in a tip of the nozzle and the discharge
target.
As with the aforementioned electrostatic suction type fluid
discharge device, this device also achieves both the
miniaturization of nozzle and the decrease in drive voltage.
Further, this structure in which the nozzle diameter is specified
in a range from .phi.1 .mu.m to .phi.5 .mu.m securely ensures the
effect of decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage for driving nozzle is outputted under a
condition: a voltage value=V.sub.0, and an application time=t,
which are specified as: 130V<V.sub.0[1-exp(-t/RC)]<250, the
meniscus surface potential of the tip of nozzle is securely set to
the value at which discharge starts or to a greater value. This
increases reliability in drawing micro dot patterns, and ensures a
low narrow-range drive voltage.
Still another electrostatic suction type fluid discharge device
according to the present invention applies a drive voltage between
a nozzle and a discharge target by drive voltage supply means so as
to apply an electric charge to a fluid supplied into the nozzle,
and thereby discharges the fluid from a hole of the nozzle to the
discharge target, the hole of the nozzle falling within a range
between .phi.1 .mu.m and .phi.5 .mu.m in diameter, the
electrostatic suction type fluid discharge device outputting the
drive voltage under a condition: a voltage value=V.sub.0, and an
application time=t, which are specified as:
130V<V.sub.0[1-exp(-t/RC)]<250V V.sub.0<250V
where R expresses electric resistance of the fluid, and C expresses
electric capacitance between the fluid in a tip of the nozzle and
the discharge target.
As with the aforementioned electrostatic suction type fluid
discharge devices, this device also achieves both the
miniaturization of nozzle and the decrease in drive voltage.
Further, this structure in which the nozzle diameter is specified
in a range from .phi.1 .mu.m to .phi.5 .mu.m securely ensures the
effect of decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage for driving nozzle is outputted under a
condition: a voltage value=V.sub.0, and an application time=t,
which are specified as: 130V<V.sub.0[1-exp(-t/RC)]<250, the
meniscus surface potential of the tip of nozzle is securely set to
the value to induce discharge or greater. This increases
reliability in drawing micro dot patterns, and ensures a low
narrow-range drive voltage.
Further, with this arrangement in which the application voltage
V.sub.0 is set to 250V or less, the degree of variation of meniscus
surface potential decreases. As a result, the variation in meniscus
surface potential due to variation in nozzle-substrate distance is
suppressed, allowing stable discharge of a micro droplet which is
required to form a micro pattern on a componential member serves as
a discharge target.
Yet another electrostatic suction type fluid discharge device
according to the present invention applies a drive voltage between
a nozzle and a discharge target by drive voltage supply means so as
to apply an electric charge to a fluid supplied into the nozzle,
and thereby discharges the fluid from a hole of the nozzle to the
discharge target, the hole of the nozzle falling within a range
between .phi.1 .mu.m and .phi.5 .mu.m in diameter, the
electrostatic suction type fluid discharge device is arranged to
satisfy: VH=-0.001X.sup.2+0.44X+125 VL=-0.0013X.sup.2+0.69X+160
where X expresses a distance between the nozzle and the discharge
target, and VH and VL express maximum and minimum values of
discharge start voltage at which discharge of the fluid from the
nozzle is started, respectively.
As with the aforementioned electrostatic suction type fluid
discharge devices, this device also achieves both the
miniaturization of nozzle and the decrease in drive voltage.
Further, this structure in which the nozzle diameter is specified
in a range from .phi.1 .mu.m to .phi.5 .mu.m securely ensures the
effect of decrease in drive voltage by the use of a micro diameter
nozzle.
Further, since the voltage at which the fluid is discharged from
the nozzle is set between the maximum value (VH) and the minimum
value (VL), which are specified as VH=-0.001X.sup.2+0.44X+125 and
VL=-0.0013X.sup.2+0.69X+160, it is possible to perform stable and
reliable discharge of fluid from the nozzle in forming a micro
pattern.
The embodiments and concrete examples of implementation discussed
in the foregoing detailed explanation serve solely to illustrate
the technical details of the present invention, which should not be
narrowly interpreted within the limits of such embodiments and
concrete examples, but rather may be applied in many variations
within the spirit of the present invention, provided such
variations do not exceed the scope of the patent claims set forth
below.
Industrial Applicability
Since the present invention allows formation of a micro dot or a
micro wire pattern on a substrate, it is typically applicable to
patterning process in manufacturing of flat displays such as a
liquid crystal display, a plasma display, an electroluminescence
display etc., or to manufacturing of semiconductor device,
formation of conductor pattern for a printed circuit board, or the
like.
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